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overview the us government 's decision to develop a hydrogen bomb , first tested in 1952 , committed the united states to an ever-escalating arms race with the soviet union . the arms race led many americans to fear that nuclear war could happen at any time , and the us government urged citizens to prepare to survive an atomic bomb . in 1950 , the us national security council released nsc-68 , a secret policy paper that called for quadrupling defense spending in order to meet the perceived soviet threat . nsc-68 would define us defense strategy throughout the cold war . president eisenhower attempted to cut defense spending by investing in a system of `` massive retaliation , '' hoping that the prospect of `` mutually-assured destruction '' from a large nuclear arsenal would deter potential aggressors . the doomsday clock and the h-bomb shortly after the us dropped the atomic bomb on japan , the scientists who had developed the bomb formed the bulletin of the atomic scientists , an organization dedicated to alerting the world to the dangers of nuclear weaponry . early contributors included j. robert oppenheimer , the director of the manhattan project , and albert einstein , who dedicated the final years of his life to promoting nuclear disarmament . in 1947 , they printed their first magazine , placing on its cover what would become an iconic symbol of the nuclear age : the doomsday clock . the clock purported to show how close humanity was to nuclear annihilation , or `` midnight . '' when the clock first appeared , the scientists predicted that humankind was mere seven minutes to midnight. $ ^1 $ but by 1953 , the scientists had revised their estimate to just two minutes to midnight . their reason for this panicked prognosis was the united states ' decision to develop and test a hydrogen bomb , or h-bomb , a nuclear weapon one thousand times more powerful than the atomic bomb that had leveled hiroshima at the end of world war ii . although scientists and some government officials argued against it , us officials ultimately reasoned that it would be imprudent for them not to develop any weapon that the soviet union might possess. $ ^2 $ the development of the h-bomb committed the us to an arms race with the ussr . despite the specter of nuclear holocaust , both the united states and the soviet union vied to build ever more powerful nuclear weapons . nsc-68 the development of the h-bomb was just part of the us project to increase its military might in this period . in 1950 , the newly-created national security council issued a report on the current state of world affairs and the steps the united states should take to confront the perceived crisis . their report , `` united states objectives and programs for national security , '' or nsc-68 , cast the tension between the us and ussr as an apocalyptic battle between good and evil . `` the issues that face us are momentous , involving the fulfillment or destruction not only of this republic but of civilization itself , '' the report began . it went on to assert that the ultimate goal of the soviet union was `` the complete subversion or forcible destruction of the machinery of government and structure of society in the countries of the non-soviet world and their replacement by an apparatus and structure subservient to and controlled from the kremlin . '' the report concluded by recommending that united states vastly increase its investment in national security , quadrupling its annual defense spending to \ $ 50 billion per year . although at first this proposal seemed both expensive and impractical , the us entry into the korean war just two months later put nsc-68 's plans in motion. $ ^3 $ nsc-68 became the cornerstone of us national security policy during the cold war , but it was a flawed document in many ways . for one thing , it assumed two `` worst-case '' scenarios : that the soviet union had both the capacity and the desire to take over the world — neither of which was necessarily true. $ ^4 $ atomic fears with both the us and ussr stockpiling nuclear weapons , american society and culture in the 1950s was pervaded by fears of nuclear warfare . schools began issuing dog tags to students so that their families could identify their bodies in the event of an attack . the us government provided instructions for building and equipping bomb shelters in basements or backyards , and some cities constructed municipal shelters . nuclear bomb drills became a routine part of disaster preparedness. $ ^5 $ the civil defense film duck and cover , first screened in 1952 , sought to help schoolchildren protect themselves from injury during a nuclear attack by instructing them to find shelter and cover themselves to prevent burns . though `` ducking and covering '' hardly would have helped to prevent serious injury in a real atomic bombing , these rehearsals for disaster at least gave american citizens an illusion of control in the face of atomic warfare. $ ^6 $ duck and cover , directed by anthony rizzo ( archer productions , 1951 ) , was a civil defense film designed to help schoolchildren react to a nuclear bomb . massive retaliation one problem with the enormous military buildup prescribed by nsc-68 was its expense . although the economic prosperity of the 1950s seemed as if it would never end , president eisenhower hoped to cut government spending . secretary of state john foster dulles proposed a new plan for getting maximum defense capabilities at an affordable cost : massive retaliation . instead of focusing on conventional military forces , the us would rely on its enormous stockpile of nuclear weapons to deter its foes from aggression , on the principle that attacking the united states would result in `` mutually-assured destruction . `` $ ^7 $ unfortunately , massive retaliation was a sledgehammer , not a scalpel . because it dealt in worst-case scenarios , it presented no intermediate measures between all-out nuclear warfare and no response whatsoever . for example , when an uprising against soviet control broke out in hungary in 1956 , the united states feared to support it for fear of antagonizing the soviet union and triggering a nuclear war. $ ^8 $ moreover , to eisenhower 's chagrin , developing and maintaining the technology required to implement massive retaliation was in fact extremely expensive . in his farewell address , eisenhower warned of the dangers posed by the growing influence of the `` military-industrial complex , '' but was unable to slow the arms race. $ ^9 $ what do you think ? what were the assumptions underlying the national security council 's recommendations in nsc-68 ? were those assumptions justified ? did civil defense films like duck and cover comfort or traumatize american children ? would it have been possible to halt nuclear development , or was the creation of more and deadlier atomic bombs unavoidable ?
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early contributors included j. robert oppenheimer , the director of the manhattan project , and albert einstein , who dedicated the final years of his life to promoting nuclear disarmament . in 1947 , they printed their first magazine , placing on its cover what would become an iconic symbol of the nuclear age : the doomsday clock . the clock purported to show how close humanity was to nuclear annihilation , or `` midnight . ''
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what is `` the doomsday clock '' ?
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overview the us government 's decision to develop a hydrogen bomb , first tested in 1952 , committed the united states to an ever-escalating arms race with the soviet union . the arms race led many americans to fear that nuclear war could happen at any time , and the us government urged citizens to prepare to survive an atomic bomb . in 1950 , the us national security council released nsc-68 , a secret policy paper that called for quadrupling defense spending in order to meet the perceived soviet threat . nsc-68 would define us defense strategy throughout the cold war . president eisenhower attempted to cut defense spending by investing in a system of `` massive retaliation , '' hoping that the prospect of `` mutually-assured destruction '' from a large nuclear arsenal would deter potential aggressors . the doomsday clock and the h-bomb shortly after the us dropped the atomic bomb on japan , the scientists who had developed the bomb formed the bulletin of the atomic scientists , an organization dedicated to alerting the world to the dangers of nuclear weaponry . early contributors included j. robert oppenheimer , the director of the manhattan project , and albert einstein , who dedicated the final years of his life to promoting nuclear disarmament . in 1947 , they printed their first magazine , placing on its cover what would become an iconic symbol of the nuclear age : the doomsday clock . the clock purported to show how close humanity was to nuclear annihilation , or `` midnight . '' when the clock first appeared , the scientists predicted that humankind was mere seven minutes to midnight. $ ^1 $ but by 1953 , the scientists had revised their estimate to just two minutes to midnight . their reason for this panicked prognosis was the united states ' decision to develop and test a hydrogen bomb , or h-bomb , a nuclear weapon one thousand times more powerful than the atomic bomb that had leveled hiroshima at the end of world war ii . although scientists and some government officials argued against it , us officials ultimately reasoned that it would be imprudent for them not to develop any weapon that the soviet union might possess. $ ^2 $ the development of the h-bomb committed the us to an arms race with the ussr . despite the specter of nuclear holocaust , both the united states and the soviet union vied to build ever more powerful nuclear weapons . nsc-68 the development of the h-bomb was just part of the us project to increase its military might in this period . in 1950 , the newly-created national security council issued a report on the current state of world affairs and the steps the united states should take to confront the perceived crisis . their report , `` united states objectives and programs for national security , '' or nsc-68 , cast the tension between the us and ussr as an apocalyptic battle between good and evil . `` the issues that face us are momentous , involving the fulfillment or destruction not only of this republic but of civilization itself , '' the report began . it went on to assert that the ultimate goal of the soviet union was `` the complete subversion or forcible destruction of the machinery of government and structure of society in the countries of the non-soviet world and their replacement by an apparatus and structure subservient to and controlled from the kremlin . '' the report concluded by recommending that united states vastly increase its investment in national security , quadrupling its annual defense spending to \ $ 50 billion per year . although at first this proposal seemed both expensive and impractical , the us entry into the korean war just two months later put nsc-68 's plans in motion. $ ^3 $ nsc-68 became the cornerstone of us national security policy during the cold war , but it was a flawed document in many ways . for one thing , it assumed two `` worst-case '' scenarios : that the soviet union had both the capacity and the desire to take over the world — neither of which was necessarily true. $ ^4 $ atomic fears with both the us and ussr stockpiling nuclear weapons , american society and culture in the 1950s was pervaded by fears of nuclear warfare . schools began issuing dog tags to students so that their families could identify their bodies in the event of an attack . the us government provided instructions for building and equipping bomb shelters in basements or backyards , and some cities constructed municipal shelters . nuclear bomb drills became a routine part of disaster preparedness. $ ^5 $ the civil defense film duck and cover , first screened in 1952 , sought to help schoolchildren protect themselves from injury during a nuclear attack by instructing them to find shelter and cover themselves to prevent burns . though `` ducking and covering '' hardly would have helped to prevent serious injury in a real atomic bombing , these rehearsals for disaster at least gave american citizens an illusion of control in the face of atomic warfare. $ ^6 $ duck and cover , directed by anthony rizzo ( archer productions , 1951 ) , was a civil defense film designed to help schoolchildren react to a nuclear bomb . massive retaliation one problem with the enormous military buildup prescribed by nsc-68 was its expense . although the economic prosperity of the 1950s seemed as if it would never end , president eisenhower hoped to cut government spending . secretary of state john foster dulles proposed a new plan for getting maximum defense capabilities at an affordable cost : massive retaliation . instead of focusing on conventional military forces , the us would rely on its enormous stockpile of nuclear weapons to deter its foes from aggression , on the principle that attacking the united states would result in `` mutually-assured destruction . `` $ ^7 $ unfortunately , massive retaliation was a sledgehammer , not a scalpel . because it dealt in worst-case scenarios , it presented no intermediate measures between all-out nuclear warfare and no response whatsoever . for example , when an uprising against soviet control broke out in hungary in 1956 , the united states feared to support it for fear of antagonizing the soviet union and triggering a nuclear war. $ ^8 $ moreover , to eisenhower 's chagrin , developing and maintaining the technology required to implement massive retaliation was in fact extremely expensive . in his farewell address , eisenhower warned of the dangers posed by the growing influence of the `` military-industrial complex , '' but was unable to slow the arms race. $ ^9 $ what do you think ? what were the assumptions underlying the national security council 's recommendations in nsc-68 ? were those assumptions justified ? did civil defense films like duck and cover comfort or traumatize american children ? would it have been possible to halt nuclear development , or was the creation of more and deadlier atomic bombs unavoidable ?
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when the clock first appeared , the scientists predicted that humankind was mere seven minutes to midnight. $ ^1 $ but by 1953 , the scientists had revised their estimate to just two minutes to midnight . their reason for this panicked prognosis was the united states ' decision to develop and test a hydrogen bomb , or h-bomb , a nuclear weapon one thousand times more powerful than the atomic bomb that had leveled hiroshima at the end of world war ii . although scientists and some government officials argued against it , us officials ultimately reasoned that it would be imprudent for them not to develop any weapon that the soviet union might possess. $ ^2 $ the development of the h-bomb committed the us to an arms race with the ussr .
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is it possible in any way to protect ourselves if a bomb does fall ?
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overview the us government 's decision to develop a hydrogen bomb , first tested in 1952 , committed the united states to an ever-escalating arms race with the soviet union . the arms race led many americans to fear that nuclear war could happen at any time , and the us government urged citizens to prepare to survive an atomic bomb . in 1950 , the us national security council released nsc-68 , a secret policy paper that called for quadrupling defense spending in order to meet the perceived soviet threat . nsc-68 would define us defense strategy throughout the cold war . president eisenhower attempted to cut defense spending by investing in a system of `` massive retaliation , '' hoping that the prospect of `` mutually-assured destruction '' from a large nuclear arsenal would deter potential aggressors . the doomsday clock and the h-bomb shortly after the us dropped the atomic bomb on japan , the scientists who had developed the bomb formed the bulletin of the atomic scientists , an organization dedicated to alerting the world to the dangers of nuclear weaponry . early contributors included j. robert oppenheimer , the director of the manhattan project , and albert einstein , who dedicated the final years of his life to promoting nuclear disarmament . in 1947 , they printed their first magazine , placing on its cover what would become an iconic symbol of the nuclear age : the doomsday clock . the clock purported to show how close humanity was to nuclear annihilation , or `` midnight . '' when the clock first appeared , the scientists predicted that humankind was mere seven minutes to midnight. $ ^1 $ but by 1953 , the scientists had revised their estimate to just two minutes to midnight . their reason for this panicked prognosis was the united states ' decision to develop and test a hydrogen bomb , or h-bomb , a nuclear weapon one thousand times more powerful than the atomic bomb that had leveled hiroshima at the end of world war ii . although scientists and some government officials argued against it , us officials ultimately reasoned that it would be imprudent for them not to develop any weapon that the soviet union might possess. $ ^2 $ the development of the h-bomb committed the us to an arms race with the ussr . despite the specter of nuclear holocaust , both the united states and the soviet union vied to build ever more powerful nuclear weapons . nsc-68 the development of the h-bomb was just part of the us project to increase its military might in this period . in 1950 , the newly-created national security council issued a report on the current state of world affairs and the steps the united states should take to confront the perceived crisis . their report , `` united states objectives and programs for national security , '' or nsc-68 , cast the tension between the us and ussr as an apocalyptic battle between good and evil . `` the issues that face us are momentous , involving the fulfillment or destruction not only of this republic but of civilization itself , '' the report began . it went on to assert that the ultimate goal of the soviet union was `` the complete subversion or forcible destruction of the machinery of government and structure of society in the countries of the non-soviet world and their replacement by an apparatus and structure subservient to and controlled from the kremlin . '' the report concluded by recommending that united states vastly increase its investment in national security , quadrupling its annual defense spending to \ $ 50 billion per year . although at first this proposal seemed both expensive and impractical , the us entry into the korean war just two months later put nsc-68 's plans in motion. $ ^3 $ nsc-68 became the cornerstone of us national security policy during the cold war , but it was a flawed document in many ways . for one thing , it assumed two `` worst-case '' scenarios : that the soviet union had both the capacity and the desire to take over the world — neither of which was necessarily true. $ ^4 $ atomic fears with both the us and ussr stockpiling nuclear weapons , american society and culture in the 1950s was pervaded by fears of nuclear warfare . schools began issuing dog tags to students so that their families could identify their bodies in the event of an attack . the us government provided instructions for building and equipping bomb shelters in basements or backyards , and some cities constructed municipal shelters . nuclear bomb drills became a routine part of disaster preparedness. $ ^5 $ the civil defense film duck and cover , first screened in 1952 , sought to help schoolchildren protect themselves from injury during a nuclear attack by instructing them to find shelter and cover themselves to prevent burns . though `` ducking and covering '' hardly would have helped to prevent serious injury in a real atomic bombing , these rehearsals for disaster at least gave american citizens an illusion of control in the face of atomic warfare. $ ^6 $ duck and cover , directed by anthony rizzo ( archer productions , 1951 ) , was a civil defense film designed to help schoolchildren react to a nuclear bomb . massive retaliation one problem with the enormous military buildup prescribed by nsc-68 was its expense . although the economic prosperity of the 1950s seemed as if it would never end , president eisenhower hoped to cut government spending . secretary of state john foster dulles proposed a new plan for getting maximum defense capabilities at an affordable cost : massive retaliation . instead of focusing on conventional military forces , the us would rely on its enormous stockpile of nuclear weapons to deter its foes from aggression , on the principle that attacking the united states would result in `` mutually-assured destruction . `` $ ^7 $ unfortunately , massive retaliation was a sledgehammer , not a scalpel . because it dealt in worst-case scenarios , it presented no intermediate measures between all-out nuclear warfare and no response whatsoever . for example , when an uprising against soviet control broke out in hungary in 1956 , the united states feared to support it for fear of antagonizing the soviet union and triggering a nuclear war. $ ^8 $ moreover , to eisenhower 's chagrin , developing and maintaining the technology required to implement massive retaliation was in fact extremely expensive . in his farewell address , eisenhower warned of the dangers posed by the growing influence of the `` military-industrial complex , '' but was unable to slow the arms race. $ ^9 $ what do you think ? what were the assumptions underlying the national security council 's recommendations in nsc-68 ? were those assumptions justified ? did civil defense films like duck and cover comfort or traumatize american children ? would it have been possible to halt nuclear development , or was the creation of more and deadlier atomic bombs unavoidable ?
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did civil defense films like duck and cover comfort or traumatize american children ? would it have been possible to halt nuclear development , or was the creation of more and deadlier atomic bombs unavoidable ?
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would it have been possible to halt nuclear development , or was the creation of more and deadlier atomic bombs unavoidable ?
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overview the louisiana purchase doubled the size of the united states , reshaping the environmental and economic makeup of the country . jefferson confronted questions of presidential authority in deciding whether or not to acquire the territory , since the us constitution does not explicitly give the president the power to purchase territory . jefferson enlisted meriwether lewis and william clark to explore the new uncharted territory and secured congressional funding for their expedition . the louisiana purchase though the louisiana territory had changed hands between france and spain a number of times , in 1800 spain ceded the territory to napoleon ’ s france . napoleon , whose attention was consumed by war in europe , began to view the territory as a needless burden . in 1803 , he volunteered to sell all 828,000 square miles to the united states for the bargain price of \ $ 15 million . jefferson adhered to a strict interpretation of the constitution and believed that without a specific enumeration of his right as president to acquire the purchase , buying the louisiana territory could plausibly be unconstitutional . the federalists opposed the purchase for several reasons , chief among them the likelihood that new slave states would enter the union from the southern parts of the territory . despite federalist opposition and the contested constitutionality of the purchase , jefferson agreed to the deal , which almost doubled us territory . he said to his cabinet regarding the purchase : “ `` it is the case of a guardian , investing the money of his ward in purchasing an important adjacent territory ; & amp ; saying to him when of age , i did this for your good. ” $ ^1 $ jefferson was correct to assume that the louisiana territory would be an important element to the united states ’ future . lewis and clark 's expedition in order to explore and map all of this new territory , jefferson authorized a westward expedition led by us army volunteers captain meriwether lewis and second lieutenant william clark . their expedition lasted from 1803 to 1806 and was aided tremendously by the help of a shoshone woman , sacagawea , who served as their guide . without sacagawea ’ s immense knowledge of the land and the indian tribes that inhabited it , lewis and clark ’ s expedition could easily have met with disaster . the louisiana purchase provided popular with white americans , who were hungry for more western lands to settle . the deal helped jefferson win reelection in 1804 by a landslide . of 176 electoral votes cast , all but 14 were in his favor . the great expansion of the united states achieved by the louisiana purchase did receive criticism , though , especially from northerners who feared the addition of more slave states and a corresponding lack of representation of their interests in the north . for southern slaveholders , new western lands would be a boon ; for enslaved people , the louisiana purchase threatened to entrench and expand their suffering to western territories . environmental impacts lewis and clark made meticulous notes of any flora and fauna they encountered during their journey . enormous clouds of gnats and mosquitos swarmed about their heads as they made their way up the missouri river . they encountered ( and killed ) a variety of animals including elk , buffalo , and grizzly bears . one member of the expedition survived a rattlesnake bite . as the men collected minerals and specimens of plants and animals , the overly curious lewis sampled minerals by tasting them and became seriously ill at one point . they sketched and documented over 260 plants in their journals , a majority of them new to scientific discovery . they also made the first scientific discoveries of many bird species , reptiles , and mammals . yet as new settlers came to make their lives on the western frontier , preserving these newfound species was hardly their concern . $ ^2 $ what do you think ? why did many federalists question the constitutionality of the louisiana purchase ? make a list of the benefits and drawbacks of the louisiana purchase . if you were president jefferson , would you have decided to acquire the territory ? how did the louisiana purchase align with jefferson ’ s vision of an agrarian america ?
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their expedition lasted from 1803 to 1806 and was aided tremendously by the help of a shoshone woman , sacagawea , who served as their guide . without sacagawea ’ s immense knowledge of the land and the indian tribes that inhabited it , lewis and clark ’ s expedition could easily have met with disaster . the louisiana purchase provided popular with white americans , who were hungry for more western lands to settle .
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how did canada get the land ?
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looking deeply take a moment to really look deeply at this example of josef albers ’ extensive series , homage to the square . the composition of this painting is simple enough – four progressively smaller squares within each other , each in a different color , and all aligned closer to the bottom of the composition than to the top . so stand back from this homage to the square and look at the whole thing . what is the relationship between the squares ? are they stacked on top of each other , like cut out pieces of construction paper ? are they sinking underneath each other , as if you are looking at a painting of a tunnel ? do some appear to push toward you and others to fall away ? and how does it change between each version of the painting ? looking at the pieces , you may find that you are able to force your eyes to see a stack of blocks or a tunnel , or you may find that you are instinctively drawn to one interpretation of how the squares are arranged . this is exactly the principle that albers experimented with as he produced hundreds of variations on this theme over a period of about 25 years . these included paintings , drawings , prints , and tapestries—but each explored the same basic question : can an artist create the appearance of three dimensions , using only color relations ? the bauhaus though albers began work on the homage paintings in 1950 , he was introduced to color theory very early in his career , when he enrolled as a student at the bauhaus in 1920 . the bauhaus was a revolutionary school of art and design in germany , founded by walter gropius in 1919 . its philosophy was to integrate the principles of fine art and functional design , and many of the most important artists in europe were teachers there . when albers was a student , the foundation for all bauhaus education was the vorkurs , or preliminary course , taught by johannes itten . the course covered the fundamentals of material , composition , and color theory , and was one of the most influential and widely disseminated aspects of bauhaus curriculum . many studies done by students as part of the vorkurs can be seen in museums and exhibitions , and they often bear a resemblance to albers ’ homage paintings : a repeated series of shapes , each in different color combinations . the goal of these exercises was for the students to understand how colors related to each other . many years later , albers used the homage paintings to go into even more depth with those lessons , and bring them to audiences , as well as art students . from dessau to black mountain in 1925 , the year that the bauhaus moved from weimar to their iconic building in dessau , gropius invited albers to be the first student of the bauhaus to join the faculty . albers worked with paul klee in the stained glass workshop and was the longest-serving member of the faculty when the school was shut down by the nazis in 1933 . but the bauhaus was to be only the first of albers ’ celebrated and influential teaching positions . when that school was shut down , albers ’ and his wife , anni—herself an influential artist and bauhaus alumna—emigrated to the united states , where he was invited to teach at the revolutionary black mountain college in north carolina , and later yale university , where he began the first homage paintings in 1950 . an encouraging but strict teacher , albers brought bauhaus ideas to a new country , introducing his disciplined approach to color theory to the next generation of the artistic vanguard in america . for all their variety of color , the homage paintings are relatively cold and clinical . it is interesting to compare them to paintings by mark rothko , who produces canvasses that have strong similarities to the homage series . albers and rothko both use roughly square or rectangular forms in solid colors , and both take the relationship between colors as their subject matter . but while rothko ’ s paintings use variation of color to suggest or inspire certain emotional reactions , albers ’ paintings are exploring the creation of space through the use of color . he experiments with subverting the limits of two-dimensional space . tradition and variation the idea of creating space through color goes back to a technique known as atmospheric perspective . the best examples can be seen in landscapes of the dutch golden age and italian renaissance artists such as leonardo da vinci . the principle of atmospheric perspective is that objects that are far away are less saturated in color , and have less contrast . looking at the mountains behind leonardo ’ s virgin of the rocks , each set of mountains that is farther away is closer in color to the sky than the set of mountains in front of it . this technique had been used to create space in representative paintings going back to antiquity , but albers was revolutionary in applying it to abstract art . his experiments in the homage series paved the way for artists such as bridget riley and a whole generation of op artists , who also pushed the limits of two-dimensional media by creating large-scale optical illusions . though homage to the square may seem boring and repetitive to some , their simple beauty is often compared to classical music , like the work of bach : a study on theme and variation . `` if one says “ red ” ( the name of a color ) and there are 50 people listening , it can be expected that there will be 50 reds in their minds . and one can be sure that all these reds will be very different . '' —josef albers , interaction of color ( 1963 ) essay by shawn roggenkamp additional resources : josef and anni albers foundation holland cotter , harmony , `` harder than it looks 'josef albers in america : painting on paper , ' '' the new york times , july 26 , 2012 josef albers entry in wikipedia
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the composition of this painting is simple enough – four progressively smaller squares within each other , each in a different color , and all aligned closer to the bottom of the composition than to the top . so stand back from this homage to the square and look at the whole thing . what is the relationship between the squares ?
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where is homage to the square currently located ?
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looking deeply take a moment to really look deeply at this example of josef albers ’ extensive series , homage to the square . the composition of this painting is simple enough – four progressively smaller squares within each other , each in a different color , and all aligned closer to the bottom of the composition than to the top . so stand back from this homage to the square and look at the whole thing . what is the relationship between the squares ? are they stacked on top of each other , like cut out pieces of construction paper ? are they sinking underneath each other , as if you are looking at a painting of a tunnel ? do some appear to push toward you and others to fall away ? and how does it change between each version of the painting ? looking at the pieces , you may find that you are able to force your eyes to see a stack of blocks or a tunnel , or you may find that you are instinctively drawn to one interpretation of how the squares are arranged . this is exactly the principle that albers experimented with as he produced hundreds of variations on this theme over a period of about 25 years . these included paintings , drawings , prints , and tapestries—but each explored the same basic question : can an artist create the appearance of three dimensions , using only color relations ? the bauhaus though albers began work on the homage paintings in 1950 , he was introduced to color theory very early in his career , when he enrolled as a student at the bauhaus in 1920 . the bauhaus was a revolutionary school of art and design in germany , founded by walter gropius in 1919 . its philosophy was to integrate the principles of fine art and functional design , and many of the most important artists in europe were teachers there . when albers was a student , the foundation for all bauhaus education was the vorkurs , or preliminary course , taught by johannes itten . the course covered the fundamentals of material , composition , and color theory , and was one of the most influential and widely disseminated aspects of bauhaus curriculum . many studies done by students as part of the vorkurs can be seen in museums and exhibitions , and they often bear a resemblance to albers ’ homage paintings : a repeated series of shapes , each in different color combinations . the goal of these exercises was for the students to understand how colors related to each other . many years later , albers used the homage paintings to go into even more depth with those lessons , and bring them to audiences , as well as art students . from dessau to black mountain in 1925 , the year that the bauhaus moved from weimar to their iconic building in dessau , gropius invited albers to be the first student of the bauhaus to join the faculty . albers worked with paul klee in the stained glass workshop and was the longest-serving member of the faculty when the school was shut down by the nazis in 1933 . but the bauhaus was to be only the first of albers ’ celebrated and influential teaching positions . when that school was shut down , albers ’ and his wife , anni—herself an influential artist and bauhaus alumna—emigrated to the united states , where he was invited to teach at the revolutionary black mountain college in north carolina , and later yale university , where he began the first homage paintings in 1950 . an encouraging but strict teacher , albers brought bauhaus ideas to a new country , introducing his disciplined approach to color theory to the next generation of the artistic vanguard in america . for all their variety of color , the homage paintings are relatively cold and clinical . it is interesting to compare them to paintings by mark rothko , who produces canvasses that have strong similarities to the homage series . albers and rothko both use roughly square or rectangular forms in solid colors , and both take the relationship between colors as their subject matter . but while rothko ’ s paintings use variation of color to suggest or inspire certain emotional reactions , albers ’ paintings are exploring the creation of space through the use of color . he experiments with subverting the limits of two-dimensional space . tradition and variation the idea of creating space through color goes back to a technique known as atmospheric perspective . the best examples can be seen in landscapes of the dutch golden age and italian renaissance artists such as leonardo da vinci . the principle of atmospheric perspective is that objects that are far away are less saturated in color , and have less contrast . looking at the mountains behind leonardo ’ s virgin of the rocks , each set of mountains that is farther away is closer in color to the sky than the set of mountains in front of it . this technique had been used to create space in representative paintings going back to antiquity , but albers was revolutionary in applying it to abstract art . his experiments in the homage series paved the way for artists such as bridget riley and a whole generation of op artists , who also pushed the limits of two-dimensional media by creating large-scale optical illusions . though homage to the square may seem boring and repetitive to some , their simple beauty is often compared to classical music , like the work of bach : a study on theme and variation . `` if one says “ red ” ( the name of a color ) and there are 50 people listening , it can be expected that there will be 50 reds in their minds . and one can be sure that all these reds will be very different . '' —josef albers , interaction of color ( 1963 ) essay by shawn roggenkamp additional resources : josef and anni albers foundation holland cotter , harmony , `` harder than it looks 'josef albers in america : painting on paper , ' '' the new york times , july 26 , 2012 josef albers entry in wikipedia
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looking deeply take a moment to really look deeply at this example of josef albers ’ extensive series , homage to the square . the composition of this painting is simple enough – four progressively smaller squares within each other , each in a different color , and all aligned closer to the bottom of the composition than to the top .
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how many homage to the square did albers create in his lifetime ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture .
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were people not supposed to be baptized before being a member of the church ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation .
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i have heard that the early christian house church is called a titulus , is this correct ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful .
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what is a `` mystery religion '' ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries .
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thank you for the article , can you tell me how did the basilica look like ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function .
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and when does the physical transformation from basilica to a church happened if there is any ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries .
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i read once that the height of ceilings in old st.peters basilica were used to make those entering to feel small compared to god or to draw the eye to the heavens ... what are some characteristics of old st. peters basilica which represent or illustrate its culture of time in history ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment .
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why is christianity constintly reffered to as a mysterie religion ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man .
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what influence from art and/or culture did christianity have on the roman empire ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior .
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little confused can someone help me answer this ... to what extent was the development of christian art and architecture influenced by the art and architecture of classical rome ?
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by the beginning of the fourth century christianity was a growing mystery religion in the cities of the roman world . it was attracting converts from different social levels . christian theology and art was enriched through the cultural interaction with the greco-roman world . but christianity would be radically transformed through the actions of a single man . rome becomes christian and constantine builds churches in 312 , the emperor constantine defeated his principal rival maxentius at the battle of the milvian bridge . accounts of the battle describe how constantine saw a sign in the heavens portending his victory . eusebius , constantine 's principal biographer , describes the sign as the chi rho , the first two letters in the greek spelling of the name christos . after that victory constantine became the principal patron of christianity . in 313 he issued the edict of milan which granted religious toleration . although christianity would not become the official religion of rome until the end of the fourth century , constantine 's imperial sanction of christianity transformed its status and nature . neither imperial rome or christianity would be the same after this moment . rome would become christian , and christianity would take on the aura of imperial rome . the transformation of christianity is dramatically evident in a comparison between the architecture of the pre-constantinian church and that of the constantinian and post-constantinian church . during the pre-constantinian period , there was not much that distinguished the christian churches from typical domestic architecture . a striking example of this is presented by a christian community house , from the syrian town of dura-europos . here a typical home has been adapted to the needs of the congregation . a wall was taken down to combine two rooms : this was undoubtedly the room for services . it is significant that the most elaborate aspect of the house is the room designed as a baptistry . this reflects the importance of the sacrament of baptism to initiate new members into the mysteries of the faith . otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire . we have already observed the role of the public cults in defining one 's civic identity , and emperors understood the construction of temples as testament to their pietas , or respect for the customary religious practices and traditions . so it was natural for constantine to want to construct edifices in honor of christianity . he built churches in rome including the church of st. peter , he built churches in the holy land , most notably the church of the nativity in bethlehem and the church of the holy sepulcher in jerusalem , and he built churches in his newly-constructed capital of constantinople . the basilica in creating these churches , constantine and his architects confronted a major challenge : what should be the physical form of the church ? clearly the traditional form of the roman temple would be inappropriate both from associations with pagan cults but also from the difference in function . temples served as treasuries and dwellings for the cult ; sacrifices occurred on outdoor altars with the temple as a backdrop . this meant that roman temple architecture was largely an architecture of the exterior . since christianity was a mystery religion that demanded initiation to participate in religious practices , christian architecture put greater emphasis on the interior . the christian churches needed large interior spaces to house the growing congregations and to mark the clear separation of the faithful from the unfaithful . at the same time , the new christian churches needed to be visually meaningful . the buildings needed to convey the new authority of christianity . these factors were instrumental in the formulation during the constantinian period of an architectural form that would become the core of christian architecture to our own time : the christian basilica . the basilica was not a new architectural form . the romans had been building basilicas in their cities and as part of palace complexes for centuries . a particularly lavish one was the so-called basilica ulpia constructed as part of the forum of the emperor trajan in the early second century . basilicas had diverse functions but essentially they served as formal public meeting places . one of the major functions of the basilicas was as a site for law courts . these were housed in an architectural form known as the apse . in the basilica ulpia , these semi-circular forms project from either end of the building , but in some cases , the apses would project off of the length of the building . the magistrate who served as the representative of the authority of the emperor would sit in a formal throne in the apse and issue his judgments . this function gave an aura of political authority to the basilicas . aula palatina , trier , early 4th century c.e . ( photo : beth m527 , cc by-nc 2.0 ) the basilica at trier ( aula palatina ) basilicas also served as audience halls as a part of imperial palaces . a well-preserved example is found in the northern german town of trier . constantine built a basilica as part of a palace complex in trier which served as his northern capital . although a fairly simple architectural form and now stripped of its original interior decoration , the basilica must have been an imposing stage for the emperor . imagine the emperor dressed in imperial regalia marching up the central axis as he makes his dramatic adventus or entrance along with other members of his court . this space would have humbled an emissary who approached the enthroned emperor seated in the apse . essay by dr. allen farber additional resources : dura europos ( yale university ) dura europos : crossroads of cultures
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otherwise this building would not stand out from the other houses . this domestic architecture obviously would not meet the needs of constantine 's architects . emperors for centuries had been responsible for the construction of temples throughout the roman empire .
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i do n't know if its the ex of catacomb of priscilla or the architecture after constantine ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) .
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if in fact these were used in the hand and did n't have a handle like our modern axes then which side would the user hold ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years .
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is potassium-argon dating more accurate then carbon dating ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years .
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when would the use of potassium-argon dating be appropriate ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range .
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is it possible for us to find some objects even older than this one ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge .
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if no , would it be possible for archaeologists to ask/assume that our ancestors had created tools long time before 2 million years ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools .
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follow-up question : if there are no individual decorations , is this really `` the beginnings of the artistic sense unique to humans '' ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand .
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if there are individual differences between the handaxes , were these made for aesthetic or practical purposes ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum .
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how durable is that material ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum .
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why are there so few art works from african cultures ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum .
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how many cultures are in african ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations .
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i thougth the evolution to homo sapiens occured sometime around 500 000 to 200 000 years ago , so who were these ancestors who made these tools and were there several species that did use tools or was it just one that gave rise to homo sapiens ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ?
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i just wonder , could these tool be sharp enough to cut hairs or shave ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum .
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since rock and stone are not raw materials , why are n't we finding more prehistoric tools like in riverbeds and even our own backyards ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) .
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there were a lot of people whom could have had stone weapons , so why are n't we finding more , and why is it such a big deal to find one ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years .
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how old is the world ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) .
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did the indians later in life end up using the same type of stones ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ?
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is there any figures that shows the difference between the humanly made handaxe and the nature made rocks ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years .
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how can you say the earth is something billion years old when there is evidence for only 6,000 year of earth as a planet ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks .
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what is bone marrow fat , and how can it be in your bones ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force .
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in all what would you think you would carve in a rock and why ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years .
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i 'm am very curious as to how these archeologists are able to know how old this artifacts are ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand .
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where did you find the stone tool in the picture ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ?
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how are we certain of the handaxe 's age ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum .
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when did the first african civilizations appear ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge .
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how did the caveman sharpen the point on the tools ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand .
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is the stone axe really technology ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force .
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what kind of rock is it that is in the picture ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum .
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it begs the question why did it take so long for humans to evolve to more complex and technological tools sooner ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand .
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how old is the stone ?
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made nearly two million years ago , stone tools such as this are the first known technological invention . this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom . this and other tools are dated to about 1.8 million years . using another hard stone as a hammer , the maker has knocked flakes off both sides of a basalt ( volcanic lava ) pebble so that they intersect to form a sharp edge . this could be used to chop branches from trees , cut meat from large animals or smash bones for marrow fat—an essential part of the early human diet . the flakes could also have been used as small knives for light duty tasks . deliberate shaping to some people this artifact might appear crude ; how can we even be certain that it is humanly made and not just bashed in rock falls or by trampling animals ? a close look reveals that the edge is formed by a deliberate sequence of skillfully placed blows of more or less uniform force . many objects of the same type , made in the same way , occur in groups called assemblages which are occasionally associated with early human remains . by contrast , natural forces strike randomly and with variable force ; no pattern , purpose or uniformity can be seen in the modifications they cause . chopping tools and flakes from the earliest african sites were referred to as oldowan by the archaeologist louis leakey . he found this example on his first expedition to olduvai in 1931 , when he was sponsored by the british museum . handaxes were still in use there some 500,000 years ago , by which time their manufacture and use had spread throughout africa , south asia , the middle east and europe where they were still being made 40,000 years ago . they have even been found as far east as korea in recent excavations . no other cultural artifact is known to have been made for such a long time across such a huge geographical range . handaxes are always made from stone and were held in the hand during use . many have this characteristic teardrop or pear shape which might have been inspired by the outline of the human hand . the beginnings of an artistic sense ? although handaxes were used for a variety of everyday tasks including all aspects of skinning and butchering an animal or working other materials such as wood , this example is much bigger than the usual useful size of such hand held tools . despite its symmetry and regular edges it appears difficult to use easily . as language began to develop along with tool making , was this handaxe made to suggest ideas ? does the care and craftsmanship with which it was made indicate the beginnings of the artistic sense unique to humans ? suggested readings : l.s.b . leakey , olduvai gorge ( cambridge , university press , 1951 ) . k.d . schick and n. schick , making silent stones speak . human evolution and the dawn of technology ( london , weidenfeld and nicolson , 1993 ) . © trustees of the british museum
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this chopping tool and others like it are the oldest objects in the british museum . it comes from an early human campsite in the bottom layer of deposits in olduvai gorge , tanzania . potassium-argon dating indicates that this bed is between 1.6 and 2.2 million years old from top to bottom .
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how did the early humans find it ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) .
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what is a good way to memorize the placement of the chromatids during separate phases ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid .
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in meosis 2 when did the chromosomes duplicate ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! )
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what 's the difference between chiasmata and the synaptonemal complex ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome .
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so at the end of meiosis , how many chromosomes do the new cells end up with , in comparison to the cell that it started with ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes .
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if the starting cell has 46 chromosomes , then how can it produce four cells with 23 chromosomes ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase .
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why is interphase not included as a stage of cell-division in both mitosis & meiosis ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . ''
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in meiosis 1 , what does g1 , s phase and g2 stand for again ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid .
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when the new nuclear membrane forms around the chromosomes , how does the cell make sure the centrosomes are outside the nucleus and all chromosomes are inside ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes .
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could you tell me what 's the different between mitosis and meiosis beside the result/product ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis .
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why are gametes haploid if they have half of a complete set of chromosomes ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed .
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because how can a haploid cell , ( with only twenty three chromatids ) split to make more haploid cells which also have twenty three chromatids ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes .
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would haploid mean there is half of what there was in the diploid cell ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid .
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how many chromosomes would there be at that point ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase .
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are there visible centrioles at telophase ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs .
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does in a normal body cell all chromosomes are single structured ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid .
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does 2n means 46 single structured chromosomes or 23 double structured chromosomes ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed .
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in the first paragraph in meiosis ii , why are the cells considered haploid if they are complete chromosomes ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life .
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is independent segregation the same as independent assortment ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna .
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on the image for telophase 1 , should n't it be diploid ( n=2 ) instead of haploid ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . ''
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why after meiosis i the cells are haploid when dna are copied before division ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i .
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and why are they haploid after division in meiosis ii ( in the picture phases of meiosis ii , it stated that starting cells are haploid and gametes are haploid as well ) ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . ''
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the stage between meiosis one and meiosis 2 is called ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs .
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how many dna molecules will the cell have in s ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell .
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what happens if there are problems in anaphase i.e when a cell gets one extra chromosome or does n't get a chromosome ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . ''
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if dna is replicated during interphase before meiosis i why are the cells haploid and not diploid at the end of meiosis i ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis .
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what are the two advantages of possessing two sets of chromosomes ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell .
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in metaphase ii , is there a random configuration of the chromatids as they line up ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes .
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how would this affect the genetic variability of the offspring ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes .
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would children tend to look more like the parents ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i .
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how long does the entire process of meiosis take in humans ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense .
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during prophase ii , why are they two centrosomes in each cell and why are they not at the opposite poles ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes .
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mitosis and meiosis are examples of which characteristics of life ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase .
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what is the phase between cell division when the cell copies itself ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles .
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before meosis 1 , cell has 23 pair chromosomes then how do they distribute in 2 daughter cell equally according to homologous pair separation ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task .
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do the chromosomes that switch similar genetic information switch more than one type of gene or do they switch genes multiple times with multiple genes ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid .
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why are the chromosomes different colors ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes .
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six centromeres are observed in a prophase 1 cell from a species of insect , how many pairs of chromosomes does this organism contains ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear .
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dna doubles at s-phase of meiosis then why individual chromosome present in cell nucleus do not appears `` x '' shaped in s-phase ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together .
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so what is the purpose of crossing over ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . ''
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are meiosis i and meiosis ii really two separate processes or is it just split for ease of explaining ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids .
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what cells are made in meiosis that is different than when mitosis occurs ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes .
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can you have random orientation on metaphase 2 ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase .
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is it possible for a sex cell or germ cell to have a uneven number of chromosomes ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) .
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i am having a bit difficulty in understanding the pattern with which the sister chromatides separated , in the second diagram of meiosis|| , as shown in the text above about meiosis , does the manner in which they are shown ( the parts of the chromatides which undergo crossing over ) , matter when indicating which side of the chromosome ( sister chromatide ) they initially where ( metaphase || ) and during separation ( anaphase || ) ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . ''
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what determines the proportion of maternal and paternal chromosomes that a meiotic product will receive after meiosis ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid .
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can there be an odd number of chromosomes at interphase ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs .
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if there are 4 unreplicated chromosomes what is the number of the haploid cell ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase .
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how does a sperm cell get its tail ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes .
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what does parthenogenesis result in females during the phases of meiosis ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life .
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and what is ( bivalent ) ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . ''
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in meiosis , where does the word `` tetrad '' come in ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis .
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are there two different stages of cytokinesis ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna .
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cytokinesis 1 and cytokinesis 2 ?
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introduction mitosis is used for almost all of your body ’ s cell division needs . it adds new cells during development and replaces old and worn-out cells throughout your life . the goal of mitosis is to produce daughter cells that are genetically identical to their mothers , with not a single chromosome more or less . meiosis , on the other hand , is used for just one purpose in the human body : the production of gametes—sex cells , or sperm and eggs . its goal is to make daughter cells with exactly half as many chromosomes as the starting cell . to put that another way , meiosis in humans is a division process that takes us from a diploid cell—one with two sets of chromosomes—to haploid cells—ones with a single set of chromosomes . in humans , the haploid cells made in meiosis are sperm and eggs . when a sperm and an egg join in fertilization , the two haploid sets of chromosomes form a complete diploid set : a new genome . phases of meiosis in many ways , meiosis is a lot like mitosis . the cell goes through similar stages and uses similar strategies to organize and separate chromosomes . in meiosis , however , the cell has a more complex task . it still needs to separate sister chromatids ( the two halves of a duplicated chromosome ) , as in mitosis . but it must also separate homologous chromosomes , the similar but nonidentical chromosome pairs an organism receives from its two parents . these goals are accomplished in meiosis using a two-step division process . homologue pairs separate during a first round of cell division , called meiosis i . sister chromatids separate during a second round , called meiosis ii . since cell division occurs twice during meiosis , one starting cell can produce four gametes ( eggs or sperm ) . in each round of division , cells go through four stages : prophase , metaphase , anaphase , and telophase . meiosis i before entering meiosis i , a cell must first go through interphase . as in mitosis , the cell grows during g $ _1 $ phase , copies all of its chromosomes during s phase , and prepares for division during g $ _2 $ phase . during prophase i , differences from mitosis begin to appear . as in mitosis , the chromosomes begin to condense , but in meiosis i , they also pair up . each chromosome carefully aligns with its homologue partner so that the two match up at corresponding positions along their full length . for instance , in the image below , the letters a , b , and c represent genes found at particular spots on the chromosome , with capital and lowercase letters for different forms , or alleles , of each gene . the dna is broken at the same spot on each homologue—here , between genes b and c—and reconnected in a criss-cross pattern so that the homologues exchange part of their dna . this process , in which homologous chromosomes trade parts , is called crossing over . it 's helped along by a protein structure called the synaptonemal complex that holds the homologues together . the chromosomes would actually be positioned one on top of the other—as in the image below—throughout crossing over ; they 're only shown side-by-side in the image above so that it 's easier to see the exchange of genetic material . you can see crossovers under a microscope as chiasmata , cross-shaped structures where homologues are linked together . chiasmata keep the homologues connected to each other after the synaptonemal complex breaks down , so each homologous pair needs at least one . it 's common for multiple crossovers ( up to $ 25 $ ! ) to take place for each homologue pair $ ^1 $ . the spots where crossovers happen are more or less random , leading to the formation of new , `` remixed '' chromosomes with unique combinations of alleles . after crossing over , the spindle begins to capture chromosomes and move them towards the center of the cell ( metaphase plate ) . this may seem familiar from mitosis , but there is a twist . each chromosome attaches to microtubules from just one pole of the spindle , and the two homologues of a pair bind to microtubules from opposite poles . so , during metaphase i , homologue pairs—not individual chromosomes—line up at the metaphase plate for separation . when the homologous pairs line up at the metaphase plate , the orientation of each pair is random . for instance , in the diagram above , the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell . but the orientation could have equally well been flipped , so that both purple chromosomes went into the cell together . this allows for the formation of gametes with different sets of homologues . in anaphase i , the homologues are pulled apart and move apart to opposite ends of the cell . the sister chromatids of each chromosome , however , remain attached to one another and do n't come apart . finally , in telophase i , the chromosomes arrive at opposite poles of the cell . in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna . meiosis ii is a shorter and simpler process than meiosis i , and you may find it helpful to think of meiosis ii as “ mitosis for haploid cells . '' the cells that enter meiosis ii are the ones made in meiosis i . these cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids . in meiosis ii , the sister chromatids separate , making haploid cells with non-duplicated chromosomes . during prophase ii , chromosomes condense and the nuclear envelope breaks down , if needed . the centrosomes move apart , the spindle forms between them , and the spindle microtubules begin to capture chromosomes . the two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles . in metaphase ii , the chromosomes line up individually along the metaphase plate . in anaphase ii , the sister chromatids separate and are pulled towards opposite poles of the cell . in telophase ii , nuclear membranes form around each set of chromosomes , and the chromosomes decondense . cytokinesis splits the chromosome sets into new cells , forming the final products of meiosis : four haploid cells in which each chromosome has just one chromatid . in humans , the products of meiosis are sperm or egg cells . how meiosis `` mixes and matches '' genes the gametes produced in meiosis are all haploid , but they 're not genetically identical . for example , take a look the meiosis ii diagram above , which shows the products of meiosis for a cell with $ 2n = 4 $ chromosomes . each gamete has a unique `` sample '' of the genetic material present in the starting cell . as it turns out , there are many more potential gamete types than just the four shown in the diagram , even for a cell with with only four chromosomes . the two main reason we can get many genetically different gametes are : crossing over . the points where homologues cross over and exchange genetic material are chosen more or less at random , and they will be different in each cell that goes through meiosis . if meiosis happens many times , as in humans , crossovers will happen at many different points . random orientation of homologue pairs . the random orientation of homologue pairs in metaphase i allows for the production of gametes with many different assortments of homologous chromosomes . in a human cell , the random orientation of homologue pairs alone allows for over $ 8 $ $ \text { million } $ different types of possible gametes $ ^7 $ . when we layer crossing over on top of this , the number of genetically different gametes that you—or any other person—can make is effectively infinite . check out the video on variation in a species to learn how genetic diversity generated by meiosis ( and fertilization ) is important in evolution and helps populations survive .
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in some organisms , the nuclear membrane re-forms and the chromosomes decondense , although in others , this step is skipped—since cells will soon go through another round of division , meiosis ii $ ^ { 2,3 } $ . cytokinesis usually occurs at the same time as telophase i , forming two haploid daughter cells . meiosis ii cells move from meiosis i to meiosis ii without copying their dna .
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if the diploid cell going through meiosis divides during interphase , how does it produce two daughter haploid cells ?
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