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And I think we can all believe that, that most of these changes are kind of benign. Maybe they just set up differently where a little pattern will show up or a little speck of pigment will show up with a slightly different color. And we even see amongst these owl butterflies, there is variation. This dude's wing is dif... | Natural Selection and the Owl Butterfly (2).mp3 |
This dude's wing is different than that guy's wing, with the commonality that they do have these eye-looking shapes. And there's not just one. There's actually multiple. This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking... | Natural Selection and the Owl Butterfly (2).mp3 |
This guy has this other thing up here that looks interesting. And they have multiple things, but the one really noticeable feature is this eye-looking thing. So how do we go from this to an eye-looking thing? So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, ... | Natural Selection and the Owl Butterfly (2).mp3 |
So the idea is you have some variation. One guy might look like that. Another guy or gal might, just randomly, their dot might be something like that. Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or... | Natural Selection and the Owl Butterfly (2).mp3 |
Another gal or guy, these wings are really badly drawn, but you get the idea. This is the butterfly's antenna right there. That's its body. Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of... | Natural Selection and the Owl Butterfly (2).mp3 |
Another person's patterns, or butterfly's patterns, might look like this. And so they're just random. But when they go into a certain environment, for whatever reason, maybe one of its predators, maybe that theory that these are supposed to look like eyes is true. And so actually, maybe this guy just has a random patte... | Natural Selection and the Owl Butterfly (2).mp3 |
And so actually, maybe this guy just has a random pattern here. And so this guy, and I'm not saying that it's definitely better, they're both going to be found and killed by predators. But it's all probabilistic. Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out o... | Natural Selection and the Owl Butterfly (2).mp3 |
Maybe this guy has a 1% less chance of getting a predator. Because when a predator just looks at them out of the corner of that eye, that little, really hazy region kind of looks like an eye. And a predator would be better off just not messing with it. And they'd rather go after the dude that looks like this. So it's j... | Natural Selection and the Owl Butterfly (2).mp3 |
And they'd rather go after the dude that looks like this. So it's just a slight probability. Now you might say, OK, what's 1% going to do? But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently.... | Natural Selection and the Owl Butterfly (2).mp3 |
But when you compound that 1% over thousands and thousands of generations, all of a sudden, this trait might dominate. And because he's just going to be killed that less frequently. 1% less frequently. Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because mayb... | Natural Selection and the Owl Butterfly (2).mp3 |
Now maybe this guy has a similar trait, but his spot is closer to the abdomen. And here it's a trade-off. Because maybe some predators get scared away by this concentration of pigment. And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this r... | Natural Selection and the Owl Butterfly (2).mp3 |
And once again, I'm not saying that we're here yet. We're not at this kind of very advanced, sophisticated pattern yet. We're at this random concentration of pigment that just shows up. So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, m... | Natural Selection and the Owl Butterfly (2).mp3 |
So we see that people who have this concentration of pigment further away from their abdomen, they do well. But when it's too close, maybe some predators think that that's actually an insect and they want to eat it. So that's actually a bad trait. So what happens is this guy dominates. And so within this population, yo... | Natural Selection and the Owl Butterfly (2).mp3 |
So what happens is this guy dominates. And so within this population, you start having a lot of variation, because he's more likely to pass on these traits. And I want to make that point very clear. This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at l... | Natural Selection and the Owl Butterfly (2).mp3 |
This isn't what happens over the course of an animal's lifetime. It's not like if somehow I experience something, or at least our current theory, if I experience something, that I can somehow pass on that knowledge to my child. What it says is if my DNA just happens to have just some variation that happens to be more u... | Natural Selection and the Owl Butterfly (2).mp3 |
So then the population, you're going to have variations within that. Maybe some guys, it's going to get a little bit look like that, maybe another one's going to look a little bit like that. Maybe there's some spots there. You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clea... | Natural Selection and the Owl Butterfly (2).mp3 |
You can kind of view it as the variation is, quote unquote, exploring. But I want to be very clear not to use any active verbs here, because this is all being done really as almost a common sense process, where everything changes. The changes that are most suited are the ones that are going to survive more frequently. ... | Natural Selection and the Owl Butterfly (2).mp3 |
And then the next generation is going to have more of that, and then you'll have variation within that change. And then this one might be like that. And maybe this is the one. These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this ... | Natural Selection and the Owl Butterfly (2).mp3 |
These were good compared to that, but now when you're competing amongst themselves, this one is able to reproduce 1% more than this guy or this guy. So this guy becomes, and maybe it's some combination of all the above, and they mix and match. It's a hugely complex system. But then this guy represents most of the popul... | Natural Selection and the Owl Butterfly (2).mp3 |
But then this guy represents most of the population. And when I say this guy, I'm saying this guy's genetic information, at least as which pertains to his wings. And then you get variation amongst that. Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of t... | Natural Selection and the Owl Butterfly (2).mp3 |
Maybe some of it, they have a little small dot, and there's some dots around it. Maybe it's like this. Maybe one of them digresses and goes back here, but then he has trouble competing, so he gets knocked out again. And then some other people have it back here. I think you get the point. That this isn't happening overn... | Natural Selection and the Owl Butterfly (2).mp3 |
And then some other people have it back here. I think you get the point. That this isn't happening overnight. These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be sign... | Natural Selection and the Owl Butterfly (2).mp3 |
These changes can be fairly incremental, but we're doing it over thousands of generations. So when you're talking about thousands of generations, or even millions of generations, even a 1% advantage can be significant. And when you accumulate those variations over a large period of time, you can get to fairly intricate... | Natural Selection and the Owl Butterfly (2).mp3 |
So I just wanted to explain that, because this is often used as, hey, sure, I can believe the butterfly moth, or I can even maybe believe the examples of the antibiotics and the bacteria or the flu. I mean, because those are kind of real-time examples. But how does something this intricate show up? And I actually want ... | Natural Selection and the Owl Butterfly (2).mp3 |
And I actually want to make a point here. We think this is more intricate because we can relate to it in our everyday lives. But if you actually look at a structure of a bacteria and how it operates, or what a virus does to infiltrate an immune system or a cell, that's actually on a lot more levels, a lot more intricat... | Natural Selection and the Owl Butterfly (2).mp3 |
In fact, the whole reason why I'm using this as an example is because this is a fairly simple example, as opposed to kind of explaining the metabolism of a certain type of bacteria and how that might change and how it might become immune to penicillin or whatever else. But I want to make this very clear that these very... | Natural Selection and the Owl Butterfly (2).mp3 |
No, it happens over large periods of time. Although there might be some little weird hormonal change that does this, but I'm not going to go there. But that is possible. But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not... | Natural Selection and the Owl Butterfly (2).mp3 |
But I just want to make this point because I think the more examples we see, the more it'll kind of hit home that this is a passive process. We're not talking about these things happening overnight. And it's actually really interesting to kind of look at our world around us and look at ecosystems as they are today, and... | Natural Selection and the Owl Butterfly (2).mp3 |
For example, are things, are traits that occur after reproduction selected for? Well, probably not, unless they affect the reproduction of the next cycle. For example, you might say, oh, well, the trait to be nurturing after reproductive years, that's after reproductive years. No, but it helps your offspring reproduce.... | Natural Selection and the Owl Butterfly (2).mp3 |
If we think about our biodiversity tutorials as an archipelago, then today we visit this island to discover why biodiversity is so important. In terms of biodiversity, we mean a lot of different things. In this case, we're going to talk about something that's known as species richness, because that's something that we ... | Biodiversity ecosystems and ecological networks.mp3 |
Because counting up the number of species, going out and finding out how many species there are in a given environment is something that we can actually do. There are different species of plants, there are many different species of animals, many different species of microbes, and many different species of fungi. And th... | Biodiversity ecosystems and ecological networks.mp3 |
Eco is an interesting word. It's an ancient word that means house. So it's a system of what goes on in your house, that is, where we all live. All of these different organisms are interacting. They're behaving together. They're interacting with one another. Some of them eat each other. | Biodiversity ecosystems and ecological networks.mp3 |
All of these different organisms are interacting. They're behaving together. They're interacting with one another. Some of them eat each other. Some of them eat what others decompose into. And they, plus the physical environment or the house, form the ecosystem. Why would the number of species, in other words, species ... | Biodiversity ecosystems and ecological networks.mp3 |
Some of them eat each other. Some of them eat what others decompose into. And they, plus the physical environment or the house, form the ecosystem. Why would the number of species, in other words, species richness, be crucial to the way an ecosystem functions? What is it about the number of species that makes the ecosy... | Biodiversity ecosystems and ecological networks.mp3 |
Why would the number of species, in other words, species richness, be crucial to the way an ecosystem functions? What is it about the number of species that makes the ecosystem work better and contribute to the resiliency or the stability of the ecosystem? Scientists are really beginning to study this, and the emerging... | Biodiversity ecosystems and ecological networks.mp3 |
We can think of any ecosystem as species that network one to another. They have interactions with each other. They can be a lot of different interactions. They can live on top of one another, like certain birds nesting in trees. Or even more crucially, these things might eat one another. This is a diagram, a network di... | Biodiversity ecosystems and ecological networks.mp3 |
They can live on top of one another, like certain birds nesting in trees. Or even more crucially, these things might eat one another. This is a diagram, a network diagram, of, believe it or not, a relatively simple ecosystem in which the organisms are interacting one with the other. We can draw lines between the specie... | Biodiversity ecosystems and ecological networks.mp3 |
We can draw lines between the species to indicate those interactions. And we can make the lines directional to show that material or matter and energy are moving from one species to another. When one organism takes a bite of another, it not only gets a mouthful of matter or food, but that food contains energy. So these... | Biodiversity ecosystems and ecological networks.mp3 |
So these arrows show the direction that energy is flowing from one species to another. The most important thing about these webs is that the strength of these interactions can vary. That is, the interdependence of the organisms in the web can vary. And here's something that might be counterintuitive. These interactions... | Biodiversity ecosystems and ecological networks.mp3 |
And here's something that might be counterintuitive. These interactions become less important the more species you have within a network. You can think of it as the interactions being spread among more players. But what happens when there are fewer players? Let's say we've got a really super simple set of interactions ... | Biodiversity ecosystems and ecological networks.mp3 |
But what happens when there are fewer players? Let's say we've got a really super simple set of interactions where this owl is eating that mouse, but can also eat this squirrel. This gives the owl options. If we remove one of these, take that guy right out of there, then we only have two species that are interacting wi... | Biodiversity ecosystems and ecological networks.mp3 |
If we remove one of these, take that guy right out of there, then we only have two species that are interacting with each other. And it's really easy to disturb this system. This guy will just eat all of these guys and boom, you can cause total ecological collapse. So the higher the biodiversity or species richness in ... | Biodiversity ecosystems and ecological networks.mp3 |
So the higher the biodiversity or species richness in a system or in a network, the stronger it is, the more stable it will be because of all the additional options open to the organisms in it. Think of that old saying about putting all your eggs in one basket. Not all interactions within a given ecosystem or network a... | Biodiversity ecosystems and ecological networks.mp3 |
For example, let's imagine that somewhere in here you've got one of these guys. And he's eating plankton, the microscopic organisms living in the water. And they're going in. These guys are the producer end of things, the ones who can photosynthesize and make chemical energy from sunlight. And remember, food equals ene... | Biodiversity ecosystems and ecological networks.mp3 |
These guys are the producer end of things, the ones who can photosynthesize and make chemical energy from sunlight. And remember, food equals energy. So what we're talking about is a lot of energy flowing from the producers to the consumer, represented by Mr. Whale over here. That's what these lines represent. They rep... | Biodiversity ecosystems and ecological networks.mp3 |
That's what these lines represent. They represent the flow of energy through the ecosystem. Eventually, the whale succumbs to life and dies. And poor Mr. Whale ends up on the sea floor. Are things over at that point? Definitely not because at that point, he's going to give up stuff that ends up as part of the producer'... | Biodiversity ecosystems and ecological networks.mp3 |
And poor Mr. Whale ends up on the sea floor. Are things over at that point? Definitely not because at that point, he's going to give up stuff that ends up as part of the producer's food web. It's shown, actually we're starting to get some really great new evidence, that these events where whales fall onto the sea botto... | Biodiversity ecosystems and ecological networks.mp3 |
It's shown, actually we're starting to get some really great new evidence, that these events where whales fall onto the sea bottom start an ecosystem of their own in ways. This is known as a whale fall. Don't get under one. It's always best not to be under one. But when the whale does hit the bottom, all kinds of inter... | Biodiversity ecosystems and ecological networks.mp3 |
It's always best not to be under one. But when the whale does hit the bottom, all kinds of interesting stuff happens. Lots of organisms come and feed on the whale. There's a succession of organisms, that is, organismal communities that change over time as the condition of the whale itself changes, that turn this whale ... | Biodiversity ecosystems and ecological networks.mp3 |
There's a succession of organisms, that is, organismal communities that change over time as the condition of the whale itself changes, that turn this whale from a fleshy organism to bones, and eventually even the bones are eaten. So this huge influx of energy that the whale's been accumulating from these producers, the... | Biodiversity ecosystems and ecological networks.mp3 |
It turns out that where you get concentrated clusters of things happening in these webs, it's usually because energy is being run through the larger organisms in the system. And when you disturb a bit of that, where you've got large amounts of energy flowing through the system, you can get a real drop in ecosystem func... | Biodiversity ecosystems and ecological networks.mp3 |
Think of it a little bit like this tremendous thing that we have now, this internet. If you draw a diagram of the interactions amongst all of the servers and all of the things that push messages through the internet, there are places where that network's going to show a lot of stuff going on, a major hub in the interne... | Biodiversity ecosystems and ecological networks.mp3 |
Like Google's servers, for example. Google is going to be at the center of one of these big clusters of a lot of messages going through. Other servers may not be so important. Those servers are going to be places like my desktop where I'm just messaging my kid to tell him to come home for dinner. If you take my server ... | Biodiversity ecosystems and ecological networks.mp3 |
Those servers are going to be places like my desktop where I'm just messaging my kid to tell him to come home for dinner. If you take my server out of the system, it's not going to disturb the entire web. But you can see what happens if you suddenly take Google out of the system. You're going to greatly perturb that pa... | Biodiversity ecosystems and ecological networks.mp3 |
You're going to greatly perturb that particular ecosystem. So these webs of interaction throughout an ecosystem are really, really important. If the system is bigger with more species and more interactions, you're going to reduce the chance that a perturbation or a disturbance is going to have a really negative impact ... | Biodiversity ecosystems and ecological networks.mp3 |
The other thing about this is that all of these things are doing something different. They're all doing different things in the ecosystem. So if you imagine one of my favorite things, I love planes. Here's a complicated plane with four engines, lots of moving parts, piston engines roaring away. You've got a rudder here... | Biodiversity ecosystems and ecological networks.mp3 |
Here's a complicated plane with four engines, lots of moving parts, piston engines roaring away. You've got a rudder here. You've got ailerons. Imagine this aircraft flying along. If you take out, say, the curtains that are in the window, you're probably not going to bring the plane down. But if you do something like r... | Biodiversity ecosystems and ecological networks.mp3 |
Imagine this aircraft flying along. If you take out, say, the curtains that are in the window, you're probably not going to bring the plane down. But if you do something like remove a couple of the crucial bolts at the base of the wing here where it connects to the fuselage, then the wing's going to fall off and we're ... | Biodiversity ecosystems and ecological networks.mp3 |
These barriers can lead to divergences resulting in speciation through the restriction of gene flow. However, what we'd like to focus on here is that there's another way to really accentuate the effects of restricted gene flow, and that's something called dispersal. This is basically the way that species of plants, ani... | New localities lead to new biodiversity (2).mp3 |
Dispersal can also lead to speciation. Species like plants that have a rooted-to-the-ground or sedentary habit, like I sometimes have when there's a hockey game on, even plants have dispersal stages in the form of seeds that can be distributed in air or in water or even in and on other organisms. Bird migration is an o... | New localities lead to new biodiversity (2).mp3 |
Bird movements can easily result in the establishment of new populations of a species where they didn't exist before. But did you know that spiders can also disperse through something called ballooning? Young spiders especially can release fine silk threads that are caught by the wind, carrying the spider aloft and to ... | New localities lead to new biodiversity (2).mp3 |
There are many other examples of dispersal. The spores of fungi that blow in the wind and get up my nose and give me allergies, or a sneeze full of bacteria or viruses. Even that's a dispersal technique that has evolved among microbes that increases their ranges during cold and flu season. Things like corals, sea urchi... | New localities lead to new biodiversity (2).mp3 |
Things like corals, sea urchins, and snails also disperse. Mostly they do this during the earliest stages of their lives, drifting through the water as little larvae. These larvae can be carried significant distances and when they eventually settle down on the substrate and metamorphose or change from the juvenile disp... | New localities lead to new biodiversity (2).mp3 |
Organisms or pieces and mats of vegetation that wash into the ocean from land can harbor terrestrial organisms that go along for the ride and are taken out to sea. They may drift to new places to live and if they land and are successful, this can result in the establishment of a new population. All these events in natu... | New localities lead to new biodiversity (2).mp3 |
If the conditions are right and the organisms can continue to survive, a new population can be established in a new place. The ability to survive and reproduce in this new place is key. In the case of sexual species, individuals need to be carrying viable young when they arrive or find a member of the opposite sex with... | New localities lead to new biodiversity (2).mp3 |
If you think of a coconut, which can travel hundreds of miles floating in the ocean, washing up on a bare lava shore, it's going to have a much harder time of it than if it washes up on a sandy beach. In other words, the conditions have to be right for the establishment of a new population. In general, the greater the ... | New localities lead to new biodiversity (2).mp3 |
And this takes us to the idea of isolation. Isolation can be very obvious on islands, but it's interesting to remember that not all islands have to be in the middle of a body of water. You can have isolation among oases in a desert, for example. You can have isolation on the tops of mountains or in the valleys between ... | New localities lead to new biodiversity (2).mp3 |
You can have isolation on the tops of mountains or in the valleys between the mountains. Or you can have isolation in a fragment of rainforest that's surrounded by extensively clear-cut land. And these habitat islands can exhibit the same principles of isolation and restriction of gene flow that influence speciation. A... | New localities lead to new biodiversity (2).mp3 |
Amazing patterns of speciation can emerge in all of these systems because there are some pretty basic rules that emerge logically from thinking about islands, dispersal, and isolation, leading to an entire field of study known as island biogeography. One of these rules is that islands can be harder or easier to get to ... | New localities lead to new biodiversity (2).mp3 |
Second, the longer the island has been in existence, the more likely it is that organisms have already arrived there and the longer they have had to diverge from their parent population. That's the time factor. A third concept is that the smaller the island, the less likely it is for a species to get there in the first... | New localities lead to new biodiversity (2).mp3 |
That would be called the area factor. Fourthly, diverse environmental conditions on an island can enhance the island's biodiversity because there's a greater chance that the right climate, the right ecological resources will be present. And we can refer to this as the habitat factor. A fifth logical rule concerns the l... | New localities lead to new biodiversity (2).mp3 |
A fifth logical rule concerns the location of the island with respect to things like currents and winds that allow new energy in the form of nutrients to flow into the system, supporting ecosystem functions or increasing or decreasing the likelihood of new colonizers arriving. And I would call that the flow factor. A s... | New localities lead to new biodiversity (2).mp3 |
I'm not sure there's a name for that one, so I'm calling it the serendipity factor. An example of that might be a freak storm that carries organisms with it. You might think of other factors or tweaks to these basic rules. For example, if you throw in the fact that organisms differ greatly in their ability to disperse,... | New localities lead to new biodiversity (2).mp3 |
For example, if you throw in the fact that organisms differ greatly in their ability to disperse, you have a rich and complicated overlay of things influencing the biodiversity on any particular island and why that biodiversity can be so different from one island to the next. Here's a simplified graph that illustrates ... | New localities lead to new biodiversity (2).mp3 |
One set refers to how close or far an island might be to the mainland and how that affects the rate of colonization. And the other set refers to whether the islands are large or small and how that's related to the rate or probability of extinction. The horizontal axis represents increasing species richness. So you have... | New localities lead to new biodiversity (2).mp3 |
So you have a couple of interesting and important intersection points that mark the lower richness of a small distant island compared to that of a large nearby island. This graph incorporates a couple of other things. One is the balancing of colonization and extinction. The more crowded the island becomes, the more lik... | New localities lead to new biodiversity (2).mp3 |
The more crowded the island becomes, the more likely it is that extinctions will happen. It also summarizes the idea that large islands close to the mainland's source of new populations, places like, say, Madagascar, will have lots and lots of species. But remember that on a big island like Madagascar, we have the habi... | New localities lead to new biodiversity (2).mp3 |
Populations can disperse on the island itself, find new habitats, encounter new barriers, and all kinds of new species can arise. And if you look at what's going on in Madagascar, that's definitely true. Madagascar has lots of endemics, species that arose there and nowhere else. Also, the geologic evidence is strong th... | New localities lead to new biodiversity (2).mp3 |
Also, the geologic evidence is strong that Madagascar broke free from Africa in the past, carrying with it subsets of species that existed on Africa and then continued to diverge and evolve on Madagascar. In contrast, consider the Galapagos. This archipelago of islands is relatively far from any mainland and sprung up ... | New localities lead to new biodiversity (2).mp3 |
These remote islands had almost no life on them when they first appeared. There were fewer species arriving there, but because of the multitude of islands within the archipelago, there is subsequent speciation of populations that make it to one island and then island hop from there. Lots of island groups illustrate the... | New localities lead to new biodiversity (2).mp3 |
Hawaii and the Philippines, for example, in any of those island groupings, you can see all of these overlapping factors at work. It's a grand and beautiful view, I think, of how islands can foster the formation of new species. But the graph can also tell you something about why so many island species are in such troubl... | New localities lead to new biodiversity (2).mp3 |
The island biogeography curves summarize that as well because we've got this word in there, extinction. Many island populations are vulnerable to extinction. I've been talking about all of this with no humans involved, but if you put humans in the equation, drop them into that island ecosystem, who's to say what the di... | New localities lead to new biodiversity (2).mp3 |
In the last video, we had completed meiosis one, and now we're ready to go into meiosis two. And you might be wondering, well, hey, you know, after mitosis, we went back into our interphase. Is there kind of a rest period between our two phases of meiosis? And the answer is sometimes. There can be a rest period where y... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
And the answer is sometimes. There can be a rest period where you have an interphase two, and that will depend on the type of cell and the species and all of that, but it is possible. So I'll actually put that over here. So we could have an interphase two. So interphase two, which you could kind of view as a rest perio... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
So we could have an interphase two. So interphase two, which you could kind of view as a rest period, but then we get into meiosis two, which will allow us to complete all of meiosis. So you could imagine meiosis two starts with prophase two. And in prophase two, now I'm dealing with two cells here. So in prophase two,... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
And in prophase two, now I'm dealing with two cells here. So in prophase two, and I'm gonna do it for both of the cells that I have after I finished meiosis one. So in prophase two, so let me, that's one of the cells. I'm not gonna have space to draw it properly. So let me draw it. So let me draw this one first. So thi... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
I'm not gonna have space to draw it properly. So let me draw it. So let me draw this one first. So this is one of the cells right over here, and then this is the other cell right over here. In prophase two, just like in prophase one, and just like in prophase in mitosis, and let me write the phases here. This is propha... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
So this is one of the cells right over here, and then this is the other cell right over here. In prophase two, just like in prophase one, and just like in prophase in mitosis, and let me write the phases here. This is prophase two we're talking about. Prophase two, your nuclear envelope dissolves again. So let me show ... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
Prophase two, your nuclear envelope dissolves again. So let me show a dissolving nuclear envelope. So your nuclear envelope dissolves again. And your chromosomes, once again, condense, I guess you could say into their denser form. So it's gonna look like this, this, and this on this side. It has a little bit of the mag... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
And your chromosomes, once again, condense, I guess you could say into their denser form. So it's gonna look like this, this, and this on this side. It has a little bit of the magenta that was from the chromosomal crossover back in prophase one. And then you have this character right over here that is shorter. You have... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
And then you have this character right over here that is shorter. You have this chromosome right over here, and it had a little orange section from the chromosomal crossover, just like this. And then you have the shorter orange chromosome just like that, so they have condensed. And you've actually, each of these cells ... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
And you've actually, each of these cells now will have duplicate centrosomes. So the centrosomes have replicated, and they will start to migrate to opposite ends of the cell. So once again, very strong analogy, especially to, frankly, prophase from mitosis. So now let's keep going. We're now ready to go to metaphase tw... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
So now let's keep going. We're now ready to go to metaphase two. Metaphase two. Metaphase, metaphase two. And let me draw my two cells. So this is one of them, and this is the other. Let me draw an arrow here so you can see that we are entering into another phase. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
Metaphase, metaphase two. And let me draw my two cells. So this is one of them, and this is the other. Let me draw an arrow here so you can see that we are entering into another phase. So we are entering into another phase, metaphase two. And you can just imagine, it's very similar to what happens in metaphase and mito... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
Let me draw an arrow here so you can see that we are entering into another phase. So we are entering into another phase, metaphase two. And you can just imagine, it's very similar to what happens in metaphase and mitosis. And actually, all of meiosis two is very similar to what happens in mitosis. So in metaphase two, ... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
And actually, all of meiosis two is very similar to what happens in mitosis. So in metaphase two, our centrosomes have migrated to the poles. So our centrosomes have migrated to the poles. I'm gonna do it twice, because I'm now dealing with two different cells. My nuclear membrane is now, it's now disappeared. And I ha... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
I'm gonna do it twice, because I'm now dealing with two different cells. My nuclear membrane is now, it's now disappeared. And I have my now dense chromosomes lining up along the equator here. So this magenta one, it'll line up right over here. So it might look like that. And actually, let me draw all the magenta ones ... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
So this magenta one, it'll line up right over here. So it might look like that. And actually, let me draw all the magenta ones now, since I have my magenta color selected. So this is the longer one and this one. This had a little bit of orange in it. Let me, has a little bit of the orange here. And then I had the short... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
So this is the longer one and this one. This had a little bit of orange in it. Let me, has a little bit of the orange here. And then I had the shorter orange chromosome. Shorter orange chromosome. And on this cell, I had the longer, the larger orange chromosome. So it had a little bit of pink on it. | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
And then I had the shorter orange chromosome. Shorter orange chromosome. And on this cell, I had the longer, the larger orange chromosome. So it had a little bit of pink on it. And of course, you have your microtubules that are, I've been doing that in blue, so let me continue doing it in blue. That are pushing the cen... | Phases of meiosis II Cells MCAT Khan Academy.mp3 |
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