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The English word Alps derives from the Latin Alpes (through French). Maurus Servius Honoratus, an ancient commentator of Virgil, says in his commentary (A. X 13) that all high mountains are called Alpes by Celts. The term may be common to Italo-Celtic, because the Celtic languages have terms for high mountains derived ... |
This may be consistent with the theory that in Greek Alpes is a name of non-Indo-European origin (which is common for prominent mountains and mountain ranges in the Mediterranean region). According to the Old English Dictionary, the Latin Alpes might possibly derive from a pre-Indo-European word *alb "hill"; "Albania" ... |
It's likely[weasel words] that alb ("white") and albus have common origins deriving from the association of the tops of tall mountains or steep hills with snow. |
In modern languages the term alp, alm, albe or alpe refers to a grazing pastures in the alpine regions below the glaciers, not the peaks. An alp refers to a high mountain pasture where cows are taken to be grazed during the summer months and where hay barns can be found, and the term "the Alps", referring to the mounta... |
The Alps are a crescent shaped geographic feature of central Europe that ranges in a 800 km (500 mi) arc from east to west and is 200 km (120 mi) in width. The mean height of the mountain peaks is 2.5 km (1.6 mi). The range stretches from the Mediterranean Sea north above the Po basin, extending through France from Gre... |
The highest portion of the range is divided by the glacial trough of the Rhone valley, with the Pennine Alps from Mont Blanc to the Matterhorn and Monte Rosa on the southern side, and the Bernese Alps on the northern. The peaks in the easterly portion of the range, in Austria and Slovenia, are smaller than those in the... |
The variances in nomenclature in the region spanned by the Alps makes classification of the mountains and subregions difficult, but a general classification is that of the Eastern Alps and Western Alps with the divide between the two occurring in eastern Switzerland according to geologist Stefan Schmid, near the Splüge... |
The highest peaks of the Western Alps and Eastern Alps, respectively, are Mont Blanc, at 4,810 m (15,780 ft) and Piz Bernina at 4,049 metres (13,284 ft). The second-highest major peaks are Monte Rosa at 4,634 m (15,200 ft) and Ortler at 3,905 m (12,810 ft), respectively |
Series of lower mountain ranges run parallel to the main chain of the Alps, including the French Prealps in France and the Jura Mountains in Switzerland and France. The secondary chain of the Alps follows the watershed from the Mediterranean Sea to the Wienerwald, passing over many of the highest and most well-known pe... |
The Alps have been crossed for war and commerce, and by pilgrims, students and tourists. Crossing routes by road, train or foot are known as passes, and usually consist of depressions in the mountains in which a valley leads from the plains and hilly pre-mountainous zones. In the medieval period hospices were establish... |
Crossing the Italian-Austrian border, the Brenner Pass separates the Ötztal Alps and Zillertal Alps and has been in use as a trading route since the 14th century. The lowest of the Alpine passes at 985 m (3,232 ft), the Semmering crosses from Lower Austria to Styria; since the 12th century when a hospice was built ther... |
Important geological concepts were established as naturalists began studying the rock formations of the Alps in the 18th century. In the mid-19th century the now defunct theory of geosynclines was used to explain the presence of "folded" mountain chains but by the mid-20th century the theory of plate tectonics became w... |
The formation of the Alps (the Alpine orogeny) was an episodic process that began about 300 million years ago. In the Paleozoic Era the Pangaean supercontinent consisted of a single tectonic plate; it broke into separate plates during the Mesozoic Era and the Tethys sea developed between Laurasia and Gondwana during th... |
Under extreme compressive stresses and pressure, marine sedimentary rocks were uplifted, creating characteristic recumbent folds, or nappes, and thrust faults. As the rising peaks underwent erosion, a layer of marine flysch sediments was deposited in the foreland basin, and the sediments became involved in younger napp... |
The Alpine orogeny occurred in ongoing cycles through to the Paleogene causing differences in nappe structures, with a late-stage orogeny causing the development of the Jura Mountains. A series of tectonic events in the Triassic, Jurassic and Cretaceous periods caused different paleogeographic regions. The Alps are sub... |
According to geologist Stefan Schmid, because the Western Alps underwent a metamorphic event in the Cenozoic Era while the Austroalpine peaks underwent an event in the Cretaceous Period, the two areas show distinct differences in nappe formations. Flysch deposits in the Southern Alps of Lombardy probably occurred in th... |
Peaks in France, Italy and Switzerland lie in the "Houillière zone", which consists of basement with sediments from the Mesozoic Era. High "massifs" with external sedimentary cover are more common in the Western Alps and were affected by Neogene Period thin-skinned thrusting whereas the Eastern Alps have comparatively ... |
In simple terms the structure of the Alps consists of layers of rock of European, African and oceanic (Tethyan) origin. The bottom nappe structure is of continental European origin, above which are stacked marine sediment nappes, topped off by nappes derived from the African plate. The Matterhorn is an example of the o... |
The core regions of the Alpine orogenic belt have been folded and fractured in such a manner that erosion created the characteristic steep vertical peaks of the Swiss Alps that rise seemingly straight out of the foreland areas. Peaks such as Mont Blanc, the Matterhorn, and high peaks in the Pennine Alps, the Briançonna... |
The Union Internationale des Associations d'Alpinisme (UIAA) has defined a list of 82 "official" Alpine summits that reach at least 4,000 m (13,123 ft). The list includes not only mountains, but also subpeaks with little prominence that are considered important mountaineering objectives. Below are listed the 22 "four-t... |
While Mont Blanc was first climbed in 1786, most of the Alpine four-thousanders were climbed during the first half of the 19th century; the ascent of the Matterhorn in 1865 marked the end of the golden age of alpinism. Karl Blodig (1859–1956) was among the first to successfully climb all the major 4,000 m peaks. He com... |
The first British Mont Blanc ascent was in 1788; the first female ascent in 1819. By the mid-1850s Swiss mountaineers had ascended most of the peaks and were eagerly sought as mountain guides. Edward Whymper reached the top of the Matterhorn in 1865 (after seven attempts), and in 1938 the last of the six great north fa... |
The Alps are a source of minerals that have been mined for thousands of years. In the 8th to 6th centuries BC during the Hallstatt culture, Celtic tribes mined copper; later the Romans mined gold for coins in the Bad Gastein area. Erzberg in Styria furnishes high-quality iron ore for the steel industry. Crystals are fo... |
Alpine crystals have been studied and collected for hundreds of years, and began to be classified in the 18th century. Leonhard Euler studied the shapes of crystals, and by the 19th century crystal hunting was common in Alpine regions. David Friedrich Wiser amassed a collection of 8000 crystals that he studied and docu... |
In the Miocene Epoch the mountains underwent severe erosion because of glaciation, which was noted in the mid-19th century by naturalist Louis Agassiz who presented a paper proclaiming the Alps were covered in ice at various intervals—a theory he formed when studying rocks near his Neuchâtel home which he believed orig... |
Agassiz studied glacier movement in the 1840s at the Unteraar Glacier where he found the glacier moved 100 m (328 ft) per year, more rapidly in the middle than at the edges. His work was continued by other scientists and now a permanent laboratory exists inside a glacier under the Jungfraujoch, devoted exclusively to t... |
Glaciers pick up rocks and sediment with them as they flow. This causes erosion and the formation of valleys over time. The Inn valley is an example of a valley carved by glaciers during the ice ages with a typical terraced structure caused by erosion. Eroded rocks from the most recent ice age lie at the bottom of the ... |
Alpine glaciers can be straight rivers of ice, long sweeping rivers, spread in a fan-like shape (Piedmont glaciers), and curtains of ice that hang from vertical slopes of the mountain peaks. The stress of the movement causes the ice to break and crack loudly, perhaps explaining why the mountains were believed to be hom... |
Glaciers end in ice caves (the Rhone Glacier), by trailing into a lake or river, or by shedding snowmelt on a meadow. Sometimes a piece of glacier will detach or break resulting in flooding, property damage and loss of life. In the 17th century about 2500 people were killed by an avalanche in a village on the French-It... |
High levels of precipitation cause the glaciers to descend to permafrost levels in some areas whereas in other, more arid regions, glaciers remain above about the 3,500 m (11,483 ft) level. The 1,817 square kilometres (702 sq mi) of the Alps covered by glaciers in 1876 had shrunk to 1,342 km2 (518 sq mi) by 1973, resul... |
The Alps provide lowland Europe with drinking water, irrigation, and hydroelectric power. Although the area is only about 11 percent of the surface area of Europe, the Alps provide up to 90 percent of water to lowland Europe, particularly to arid areas and during the summer months. Cities such as Milan depend on 80 per... |
Major European rivers flow from Switzerland, such as the Rhine, the Rhone, the Inn, the Ticino and the Po, all of which have headwaters in the Alps and flow into neighbouring countries, finally emptying into the North Sea, the Mediterranean Sea, the Adriatic Sea and the Black Sea. Other rivers such as the Danube have m... |
The rivers form lakes, such as Lake Geneva, a crescent shaped lake crossing the Swiss border with Lausanne on the Swiss side and the town of Evian-les-Bains on the French side. In Germany, the medieval St. Bartholomew's chapel was built on the south side of the Königssee, accessible only by boat or by climbing over the... |
Scientists have been studying the impact of climate change and water use. For example, each year more water is diverted from rivers for snowmaking in the ski resorts, the effect of which is yet unknown. Furthermore, the decrease of glaciated areas combined with a succession of winters with lower-than-expected precipita... |
The Alps are a classic example of what happens when a temperate area at lower altitude gives way to higher-elevation terrain. Elevations around the world that have cold climates similar to those of the polar regions have been called Alpine. A rise from sea level into the upper regions of the atmosphere causes the tempe... |
The severe weather in the Alps has been studied since the 18th century; particularly the weather patterns such as the seasonal foehn wind. Numerous weather stations were placed in the mountains early in the early 20th century, providing continuous data for climatologists. Some of the valleys are quite arid such as the ... |
The areas that are not arid and receive high precipitation experience periodic flooding from rapid snowmelt and runoff. The mean precipitation in the Alps ranges from a low of 2,600 mm (100 in) per year to 3,600 mm (140 in) per year, with the higher levels occurring at high altitudes. At altitudes between 1,000 and 3,0... |
The Alps are split into five climatic zones, each with different vegetation. The climate, plant life and animal life vary among the different sections or zones of the mountains. The lowest zone is the colline zone, which exists between 500 and 1,000 m (1,640 and 3,281 ft), depending on the location. The montane zone ex... |
Various models of climate change have been projected into the 22nd century for the Alps, with an expectation that a trend toward increased temperatures will have an effect on snowfall, snowpack, glaciation, and river runoff. |
Thirteen thousand species of plants have been identified in the Alpine regions. Alpine plants are grouped by habitat and soil type which can be limestone or non-calcerous. The habitats range from meadows, bogs, woodland (deciduous and coniferous) areas to soilless scree and moraines, and rock faces and ridges. A natura... |
Above the forestry, there is often a band of short pine trees (Pinus mugo), which is in turn superseded by Alpenrosen, dwarf shrubs, typically Rhododendron ferrugineum (on acid soils) or Rhododendron hirsutum (on alkaline soils). Although the Alpenrose prefers acidic soil, the plants are found throughout the region. Ab... |
Alpine plants such the Alpine gentian grow in abundance in areas such as the meadows above the Lauterbrunnental. Gentians are named after the Illyrian king Gentius, and 40 species of the early-spring blooming flower grow in the Alps, in a range of 1,500 to 2,400 m (4,921 to 7,874 ft). Writing about the gentians in Swit... |
At these higher altitudes, the plants tend to form isolated cushions. In the Alps, several species of flowering plants have been recorded above 4,000 m (13,120 ft), including Ranunculus glacialis, Androsace alpina and Saxifraga biflora. The Eritrichium nanum, commonly known as the King of the Alps, is the most elusive ... |
The extreme and stressful climatic conditions give way to the growth of plant species with secondary metabolites important for medicinal purposes. Origanum vulgare, Prunella vulgaris, Solanum nigrum and Urtica dioica are some of the more useful medicinal species found in the Alps. |
Human interference has nearly exterminated the trees in many areas, and, except for the beech forests of the Austrian Alps, forests of deciduous trees are rarely found after the extreme deforestation between the 17th and 19th centuries. The vegetation has changed since the second half of the 20th century, as the high a... |
The Alps are a habitat for 30,000 species of wildlife, ranging from the tiniest snow fleas to brown bears, many of which have made adaptations to the harsh cold conditions and high altitudes to the point that some only survive in specific micro-climates either directly above or below the snow line. |
The largest mammal to live in the highest altitudes are the alpine ibex, which have been sighted as high as 3,000 m (9,843 ft). The ibex live in caves and descend to eat the succulent alpine grasses. Classified as antelopes, chamois are smaller than ibex and found throughout the Alps, living above the tree line and are... |
Many rodents such as voles live underground. Marmots live almost exclusively above the tree line as high as 2,700 m (8,858 ft). They hibernate in large groups to provide warmth, and can be found in all areas of the Alps, in large colonies they build beneath the alpine pastures. Golden eagles and bearded vultures are th... |
Reptiles such as adders and vipers live up to the snow line; because they cannot bear the cold temperatures they hibernate underground and soak up the warmth on rocky ledges. The high-altitude Alpine salamanders have adapted to living above the snow line by giving birth to fully developed young rather than laying eggs.... |
A number of species of moths live in the Alps, some of which are believed to have evolved in the same habitat up to 120 million years ago, long before the Alps were created. Blue moths can commonly be seen drinking from the snow melt; some species of blue moths fly as high as 1,800 m (5,906 ft). The butterflies tend to... |
Some of the species of moths and insects show evidence of having been indigenous to the area from as long ago as the Alpine orogeny. In Emosson in Valais, Switzerland, dinosaur tracks were found in the 1970s, dating probably from the Triassic Period. |
About 10,000 years ago, when the ice melted after the last glacial period, late Paleolithic communities were established along the lake shores and in cave systems. Evidence of human habitation has been found in caves near Vercors, close to Grenoble; in Austria the Mondsee culture shows evidence of houses built on piles... |
In 1991 a mummy of a neolithic body, known as Ötzi the Iceman, was discovered by hikers on the Similaun glacier. His clothing and gear indicate that he lived in an alpine farming community, while the location and manner of his death - an arrowhead was discovered in his shoulder - suggests he was travelling from one pla... |
Celtic tribes settled in Switzerland between 1000 to 1500 BC. The Raetians lived in the eastern regions, while the west was occupied by the Helvetii and the Allobrogi settled in the Rhone valley and in Savoy. Among the many substances Celtic tribes mined was salt in areas such as Salzburg in Austria where evidence of t... |
During the Second Punic War in 218 BC, the Carthaginian general Hannibal probably crossed the Alps with an army numbering 38,000 infantry, 8,000 cavalry, and 37 war elephants. This was one of the most celebrated achievements of any military force in ancient warfare, although no evidence exists of the actual crossing or... |
The Roman expansion brought the defeat of the Allobrogi in 121 BC and during the Gallic Wars in 58 BC Julius Caesar overcame the Helvetii. The Rhaetians continued to resist but were eventually conquered when the Romans turned northward to the Danube valley in Austria and defeated the Brigantes. The Romans built settlem... |
Christianity was established in the region by the Romans, and saw the establishment of monasteries and churches in the high regions. The Frankish expansion of the Carolingian Empire and the Bavarian expansion in the eastern Alps introduced feudalism and the building of castles to support the growing number of dukedoms ... |
Much of the medieval period was a time of power struggles between competing dynasties such as the House of Savoy, the Visconti in northern Italy and the House of Habsburg in Austria and Slovenia. In 1291 to protect themselves from incursions by the Habsburgs, four cantons in the middle of Switzerland drew up a charter ... |
During the Napoleonic Wars in the late 18th century and early 19th century, Napoleon annexed territory formerly controlled by the Habsburgs and Savoys. In 1798 he established the Helvetic Republic in Switzerland; two years later he led an army across the St. Bernard pass and conquered almost all of the Alpine regions. |
After the fall of Napoléon, many alpine countries developed heavy protections to prevent any new invasion. Thus, Savoy built a series of fortifications in the Maurienne valley in order to protect the major alpine passes, such as the col du Mont-Cenis that was even crossed by, Charlemagne and his father to defeat the Lo... |
In the 19th century, the monasteries built in the high Alps during the medieval period to shelter travelers and as places of pilgrimage, became tourist destinations. The Benedictines had built monasteries in Lucerne, Switzerland, and Oberammergau; the Cistercians in the Tyrol and at Lake Constance; and the Augustinians... |
Radiocarbon dated charcoal placed around 50,000 years ago was found in the Drachloch (Dragon's Hole) cave above the village of Vattis in the canton of St. Gallen, proving that the high peaks were visited by prehistoric people. Seven bear skulls from the cave may have been buried by the same prehistoric people. The peak... |
Charles VII of France ordered his chamberlain to climb Mont Aiguille in 1356. The knight reached the summit of Rocciamelone where he left a bronze triptych of three crosses, a feat which he conducted with the use of ladders to traverse the ice. In 1492 Antoine de Ville climbed Mont Aiguille, without reaching the summit... |
Conrad Gessner was the first naturalist to ascend the mountains in the 16th century, to study them, writing that in the mountains he found the "theatre of the Lord". By the 19th century more naturalists began to arrive to explore, study and conquer the high peaks; they were followed by artists, writers and painters. Tw... |
Jean-Jacques Rousseau was the first of many to present the Alps as a place of allure and beauty, banishing the prevalent conception of the mountains as a hellish wasteland inhabited by demons. Rousseau's conception of alpine purity was later emphasized with the publication of Albrecht von Haller's poem Die Alpen that d... |
In 1816 Byron, Percy Bysshe Shelley and his wife Mary Shelley visited Geneva and all three were inspired by the scenery in their writings. During these visits Shelley wrote the poem "Mont Blanc", Byron wrote "The Prisoner of Chillon" and the dramatic poem Manfred, and Mary Shelley, who found the scenery overwhelming, c... |
Austrian-born Adolf Hitler had a lifelong romantic fascination with the Alps and by the 1930s established a home in the Obersalzberg region outside of Berchtesgaden. His first visit to the area was in 1923 and he maintained a strong tie there until the end of his life. At the end of World War II the US Army occupied Ob... |
By 1940 the Third Reich had occupied many of the Alpine countries. Austria underwent a political coup that made it part of the Third Reich; France had been invaded and Italy was a fascist regime. Switzerland was the only country to luckily avoid invasion. The Swiss Confederate mobilized its troops—the country follows t... |
Ski troops were trained for the war, and battles were waged in mountainous areas such as the battle at Riva Ridge in Italy, where the American 10th Mountain Division encountered heavy resistance in February 1945. At the end of the war, a substantial amount of Nazi plunder was found stored in Austria, where Hitler had h... |
The population of the region is 14 million spread across eight countries. On the rim of the mountains, on the plateaus and the plains the economy consists of manufacturing and service jobs whereas in the higher altitudes and in the mountains farming is still essential to the economy. Farming and forestry continue to be... |
Much of the Alpine culture is unchanged since the medieval period when skills that guaranteed survival in the mountain valleys and in the highest villages became mainstays, leading to strong traditions of carpentry, woodcarving, baking and pastry-making, and cheesemaking. |
Farming had been a traditional occupation for centuries, although it became less dominant in the 20th century with the advent of tourism. Grazing and pasture land are limited because of the steep and rocky topography of the Alps. In mid-June cows are moved to the highest pastures close to the snowline, where they are w... |
Cheesemaking is an ancient tradition in most Alpine countries. A wheel of cheese from the Emmental in Switzerland can weigh up to 45 kg (100 lb), and the Beaufort in Savoy can weight up to 70 kilograms (150 lb). Owners of the cows traditionally receive from the cheesemakers a portion in relation to the proportion of th... |
In the high villages people live in homes built according to medieval designs that withstand cold winters. The kitchen is separated from the living area (called the stube, the area of the home heated by a stove), and second-floor bedrooms benefit from rising heat. The typical Swiss chalet originated in the Bernese Ober... |
Food is passed from the kitchen to the stube, where the dining room table is placed. Some meals are communal, such as fondue, where a pot is set in the middle of the table for each person to dip into. Other meals are still served in a traditional manner on carved wooden plates. Furniture has been traditionally elaborat... |
Roofs are traditionally constructed from Alpine rocks such as pieces of schist, gneiss or slate. Such chalets are typically found in the higher parts of the valleys, as in the Maurienne valley in Savoy, where the amount of snow during the cold months is important. The inclination of the roof cannot exceed 40%, allowing... |
At present the Alps are one of the more popular tourist destinations in the world with many resorts such Oberstdorf, in Bavaria, Saalbach in Austria, Davos in Switzerland, Chamonix in France, and Cortina d'Ampezzo in Italy recording more than a million annual visitors. With over 120 million visitors a year tourism is i... |
The tourism industry began in the early 19th century when foreigners visited the Alps, traveled to the bases of the mountains to enjoy the scenery, and stayed at the spa-resorts. Large hotels were built during the Belle Époque; cog-railways, built early in the 20th century, brought tourists to ever higher elevations, w... |
In the first half of the 20th century the Olympic Winter Games were held three times in Alpine venues: the 1924 Winter Olympics in Chamonix, France; the 1928 Winter Olympics in St. Moritz, Switzerland; and the 1936 Winter Olympics in Garmisch-Partenkirchen, Germany. During World War II the winter games were canceled bu... |
During the post-World War I period ski-lifts were built in Swiss and Austrian towns to accommodate winter visitors, but summer tourism continued to be important; by the mid-20th century the popularity of downhill skiing increased greatly as it became more accessible and in the 1970s several new villages were built in F... |
The region is serviced by 4,200 km (2,600 mi) of roads used by 6 million vehicles. Train travel is well established in the Alps, with, for instance 120 km (75 mi) of track for every 1,000 km2 (390 sq mi) in a country such as Switzerland. Most of Europe's highest railways are located there. Moreover, plans are underway ... |
Some high mountain villages, such as Avoriaz (in France), Wengen, and Zermatt (in Switzerland) are accessible only by cable car or cog-rail trains, and are car free. Other villages in the Alps are considering becoming car free zones or limiting the number of cars for reasons of sustainability of the fragile Alpine terr... |
The lower regions and larger towns of the Alps are well-served by motorways and main roads, but higher mountain passes and byroads, which are amongst the highest in Europe, can be treacherous even in summer due to steep slopes. Many passes are closed in winter. A multitude of airports around the Alps (and some within),... |
A gene is a locus (or region) of DNA that encodes a functional RNA or protein product, and is the molecular unit of heredity.:Glossary The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits. Most biological traits are under the influence of polygenes (many different ge... |
Genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a protein, which cause different phenotype traits. Colloquial usage of the term "having a gene" (e.g., "good genes," "hair colour gene") typically refers... |
The concept of a gene continues to be refined as new phenomena are discovered. For example, regulatory regions of a gene can be far removed from its coding regions, and coding regions can be split into several exons. Some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding ... |
The existence of discrete inheritable units was first suggested by Gregor Mendel (1822–1884). From 1857 to 1864, he studied inheritance patterns in 8000 common edible pea plants, tracking distinct traits from parent to offspring. He described these mathematically as 2n combinations where n is the number of differing ch... |
Prior to Mendel's work, the dominant theory of heredity was one of blending inheritance, which suggested that each parent contributed fluids to the fertilisation process and that the traits of the parents blended and mixed to produce the offspring. Charles Darwin developed a theory of inheritance he termed pangenesis, ... |
The word gene is derived (via pangene) from the Ancient Greek word γένος (génos) meaning "race, offspring". Gene was coined in 1909 by Danish botanist Wilhelm Johannsen to describe the fundamental physical and functional unit of heredity, while the related word genetics was first used by William Bateson in 1905. |
Advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid (DNA) was shown to be the molecular repository of genetic information by experiments in the 1940s to 1950s. The structure of DNA was studied by Rosalind Franklin using X-ray crystallography, which led James D. W... |
In 1972, Walter Fiers and his team at the University of Ghent were the first to determine the sequence of a gene: the gene for Bacteriophage MS2 coat protein. The subsequent development of chain-termination DNA sequencing in 1977 by Frederick Sanger improved the efficiency of sequencing and turned it into a routine lab... |
The theories developed in the 1930s and 1940s to integrate molecular genetics with Darwinian evolution are called the modern evolutionary synthesis, a term introduced by Julian Huxley. Evolutionary biologists subsequently refined this concept, such as George C. Williams' gene-centric view of evolution. He proposed an e... |
The vast majority of living organisms encode their genes in long strands of DNA (deoxyribonucleic acid). DNA consists of a chain made from four types of nucleotide subunits, each composed of: a five-carbon sugar (2'-deoxyribose), a phosphate group, and one of the four bases adenine, cytosine, guanine, and thymine.:2.1 |
Two chains of DNA twist around each other to form a DNA double helix with the phosphate-sugar backbone spiralling around the outside, and the bases pointing inwards with adenine base pairing to thymine and guanine to cytosine. The specificity of base pairing occurs because adenine and thymine align form two hydrogen bo... |
Due to the chemical composition of the pentose residues of the bases, DNA strands have directionality. One end of a DNA polymer contains an exposed hydroxyl group on the deoxyribose; this is known as the 3' end of the molecule. The other end contains an exposed phosphate group; this is the 5' end. The two strands of a ... |
The expression of genes encoded in DNA begins by transcribing the gene into RNA, a second type of nucleic acid that is very similar to DNA, but whose monomers contain the sugar ribose rather than deoxyribose. RNA also contains the base uracil in place of thymine. RNA molecules are less stable than DNA and are typically... |
The total complement of genes in an organism or cell is known as its genome, which may be stored on one or more chromosomes. A chromosome consists of a single, very long DNA helix on which thousands of genes are encoded.:4.2 The region of the chromosome at which a particular gene is located is called its locus. Each lo... |
The majority of eukaryotic genes are stored on a set of large, linear chromosomes. The chromosomes are packed within the nucleus in complex with storage proteins called histones to form a unit called a nucleosome. DNA packaged and condensed in this way is called chromatin.:4.2 The manner in which DNA is stored on the h... |
Prokaryotes (bacteria and archaea) typically store their genomes on a single large, circular chromosome. Similarly, some eukaryotic organelles contain a remnant circular chromosome with a small number of genes.:14.4 Prokaryotes sometimes supplement their chromosome with additional small circles of DNA called plasmids, ... |
Whereas the chromosomes of prokaryotes are relatively gene-dense, those of eukaryotes often contain regions of DNA that serve no obvious function. Simple single-celled eukaryotes have relatively small amounts of such DNA, whereas the genomes of complex multicellular organisms, including humans, contain an absolute majo... |
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