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And then a carrier protein, and the way I'm gonna draw it isn't exactly how a carrier protein would actually look, but it would hopefully give you the right idea. So maybe it's like this. Maybe it's like this. And if things wanna move down their concentration gradient, let's say you have a higher concentration above, a... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
And if things wanna move down their concentration gradient, let's say you have a higher concentration above, and I'm just gonna say some arbitrary particle has a higher concentration above than it does below, they can actually attach potentially, or kind of get into a compartment over here, and then that would trigger ... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
So it could kind of flip around. Let me get the other tool. It could, whoops, really having trouble with my tools today. All right. All right, it could flip around like this. So before it was open to the top, but now it could flip around, and the stuff that it just collected from the top could be dumped inside, inside ... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
All right. All right, it could flip around like this. So before it was open to the top, but now it could flip around, and the stuff that it just collected from the top could be dumped inside, inside the cell. And once again, this is passive transport because it's all about things moving down their concentration gradien... | Facilitated diffusion Membranes and transport Biology Khan Academy.mp3 |
Although, in, for example, the case of this character and this character, the mechanics could get quite difficult. But an interesting question is, is where do dogs come from, and why do we have these seemingly specialized breeds amongst dogs? You might have things like a Rottweiler that's better for protection. You mig... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
You might have things like Terriers that have been specialized to maybe go after rodents. You have things like Border Collies that are good at herding other types of animals. The simple answer is, through artificial selection and domestication. Remember, in any population of a species, there's variation in that species... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
Remember, in any population of a species, there's variation in that species. And when we talked about natural selection, that's where the environment might select for certain of those variants. Certain of those variants might make it a little bit easier to survive or reproduce, and then those would predominate, and tha... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
Artificial selection and domestication is where humans take matters into their own hands. And instead of waiting for nature to do things, they are the selection factor. They pick which of the species get to reproduce and which ones don't. And when you have that type of artificial selection, the change can happen much, ... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
And when you have that type of artificial selection, the change can happen much, much faster. Breeding is essentially artificial selection. So dogs like this, and all the dogs we know of, had ancestors that looked like this, that looked like a wolf, that were a wolf. And what we theorize is that the early stages of som... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
And what we theorize is that the early stages of some wolves eventually evolving into dogs might have been more traditional natural selection, where tens of thousands of years ago, our hunter-gatherer ancestors, as they hunted and gathering, they might have left over food here or there. And some of the wolves that just... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
Maybe they provide some form of protection. Maybe over time, they started breeding the wolves. So the wolves that were especially friendly, the wolves that were especially good at a certain task, say protection, or going after some type of an animal, or retrieving things, they allowed those to reproduce together, and o... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
And even once we had dogs, the breeding got even more specialized. As I mentioned, things like border collies, this was many years, many generations of breeding where sheep herders might have selected dogs that were good at herding sheep, that terriers came from dogs that were good at going after rodents, things like r... | Artificial selection and domestication Natural selection AP Biology Khan Academy.mp3 |
Allele frequency. And just as a reminder, an allele is a variant of a gene. You get a variant of a gene from your mother and you get another variant of the gene from the father. And so when we're talking about the allele, we're talking about that specific variant that you got from your mother or your father. And we've ... | Allele frequency (2).mp3 |
And so when we're talking about the allele, we're talking about that specific variant that you got from your mother or your father. And we've seen this before. But now let's dig a little bit deeper. And to help us get our heads around this, we'll start with a fairly common model for this. And we're gonna think about ey... | Allele frequency (2).mp3 |
And to help us get our heads around this, we'll start with a fairly common model for this. And we're gonna think about eye color. And obviously this is a very large simplification. But let's just assume that we have a population where there's only two variants of an eye color gene. Let's first assume there is an eye co... | Allele frequency (2).mp3 |
But let's just assume that we have a population where there's only two variants of an eye color gene. Let's first assume there is an eye color gene and let's assume there's two variants. One variant, one allele for eye color, we'll use the shorthand capital B. Let's say that's the allele for brown. Brown eye color. And... | Allele frequency (2).mp3 |
Let's say that's the allele for brown. Brown eye color. And we're gonna assume that this one is dominant. It's dominant over the other allele. Now the other allele, we're gonna assume, is for blue eye color. And we'll represent that with a lowercase b. So that is blue eye color. | Allele frequency (2).mp3 |
It's dominant over the other allele. Now the other allele, we're gonna assume, is for blue eye color. And we'll represent that with a lowercase b. So that is blue eye color. And we're going to assume that this is recessive. So once again, this is review. Someone who has one of the big B alleles, the brown alleles. | Allele frequency (2).mp3 |
So that is blue eye color. And we're going to assume that this is recessive. So once again, this is review. Someone who has one of the big B alleles, the brown alleles. It doesn't matter what their other allele is going to be because it's either gonna be another brown or it's going to be a blue. They're going to show b... | Allele frequency (2).mp3 |
Someone who has one of the big B alleles, the brown alleles. It doesn't matter what their other allele is going to be because it's either gonna be another brown or it's going to be a blue. They're going to show brown eyes. So this is going to be brown eyes. And this is going to be brown eyes because the capital B is do... | Allele frequency (2).mp3 |
So this is going to be brown eyes. And this is going to be brown eyes because the capital B is dominant. The only way to get blue eyes is to be, the only way to have blue eyes is to be a homozygote for the recessive allele. And all of that, of course, is review. We've seen that before. But now let's think about allele ... | Allele frequency (2).mp3 |
And all of that, of course, is review. We've seen that before. But now let's think about allele frequency. And to think about that, I'll set up a very artificially small population. So let's say our population has exactly two people in it. Population has exactly two people in it, person one and person two. And let's sa... | Allele frequency (2).mp3 |
And to think about that, I'll set up a very artificially small population. So let's say our population has exactly two people in it. Population has exactly two people in it, person one and person two. And let's say we're able to look into their DNA and figure out their genotypes. So person one, let's say, has a capital... | Allele frequency (2).mp3 |
And let's say we're able to look into their DNA and figure out their genotypes. So person one, let's say, has a capital B allele, has a brown allele and a blue allele. While person two has two blue alleles. Now given that we know the genotypes in this artificially small population, now we can start thinking about the a... | Allele frequency (2).mp3 |
Now given that we know the genotypes in this artificially small population, now we can start thinking about the allele frequencies or the frequencies of the different alleles. So what do you think is going to be the frequency, the frequency of the brown allele in this population? And I encourage you to pause this video... | Allele frequency (2).mp3 |
So I'm assuming you've had a go at it. So you might be tempted to say, oh, well it looks like one out of two people have it, maybe it's 50%. But that wouldn't be the right way to think about allele frequencies. And allele frequencies, you wanna dig a little bit deeper and look at the individual alleles. And when you lo... | Allele frequency (2).mp3 |
And allele frequencies, you wanna dig a little bit deeper and look at the individual alleles. And when you look at that, you say, okay, there's four individual alleles in this population of, or there's four variants in this, or there's literally four chromosomes, I guess you could say, that are carrying that gene in th... | Allele frequency (2).mp3 |
And so we could say that that is going to be 0.25, or 25%. So once again, 20, 25% of the genes for eye color have the capital B allele, have the brown allele. Now we can do the same, we can ask ourselves the same question for the lowercase b allele. What fraction of the genes in this population are code for or represen... | Allele frequency (2).mp3 |
What fraction of the genes in this population are code for or represent the lowercase b, the blue allele? And once again, I encourage you to pause the video and think about it. Well, very similar idea. There's four genes in the population that are coding for eye color. Of them, one, two, three, one, two, three, code fo... | Allele frequency (2).mp3 |
There's four genes in the population that are coding for eye color. Of them, one, two, three, one, two, three, code for or are the lowercase blue, are the lowercase blue allele. So that's 0.75, or 75%. 75% of the genes code for the lowercase, the blue allele, while 25 are the brown, are the brown allele. And I really w... | Allele frequency (2).mp3 |
75% of the genes code for the lowercase, the blue allele, while 25 are the brown, are the brown allele. And I really wanna hit this point home, how this is different than, say, the phenotype frequency. If I asked you in the population, if I asked you the percent of brown-eyed people, brown-eyed people, so now I'm talki... | Allele frequency (2).mp3 |
Well, there's two people in the population, one of them is exhibiting brown eyes, so that's going to be 1.5. And similarly, if I were to ask you what is the percentage of people who are blue-eyed? That too would be 1.5. This person is one of the two people, they're exhibiting blue eyes. But allele frequency, we're digg... | Allele frequency (2).mp3 |
This person is one of the two people, they're exhibiting blue eyes. But allele frequency, we're digging deeper. We're looking at the genotypes, and we're saying, well, out of the four genes here, one of them is the big B allele, so that's 25%, so 25% of the gene population codes for, is the brown allele, and 75% is the... | Allele frequency (2).mp3 |
And this is really important to internalize, because once we internalize this, then as we'll see, the ideas in the Hardy-Weinberg principle start to make a lot of sense. And I'll do a little bit of foreshadowing. We can denote this, and this is just a convention that's often used, by the lowercase letter p, and we can ... | Allele frequency (2).mp3 |
So p, lowercase p, is the frequency of the dominant allele, lowercase q, the frequency of the recessive allele. But what's true here? What's true of p, what's true, what's going to be true of p plus q? What's going to be, what's p plus q going to be equal to? And I encourage you to pause the video again, and think abou... | Allele frequency (2).mp3 |
What's going to be, what's p plus q going to be equal to? And I encourage you to pause the video again, and think about that. What is this going to be equal to? Well, when we started off, we said that there's only two potential, that's one of the assumptions we assumed. We assumed there's only two alleles in this popul... | Allele frequency (2).mp3 |
The whole process of natural selection is to some degree dependent on the idea of variation, that within any population of a species, you have some genetic variation. So for example, let's say I have a bunch of, well, this is the circle species. And one guy is that color, and then I've got a bunch more. Maybe some are ... | Variation in a Species (2).mp3 |
Maybe some are that color. That's the same color. That one, and that one, and that one. And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And i... | Variation in a Species (2).mp3 |
And for whatever reason, sometimes there are no environmental factors that will predispose one of these guys to be able to survive and reproduce over the other. But every now and then, there might be some environmental factor. And it makes maybe all of a sudden, this guy is more fit to reproduce. And so for whatever re... | Variation in a Species (2).mp3 |
And so for whatever reason, this guy is able to reproduce more frequently, and these guys less frequently. And some of them get killed or whatever, eaten by birds or they're just not able to reproduce for whatever reason. And then maybe these guys are something in between. And so over time, the frequency of the differe... | Variation in a Species (2).mp3 |
And so over time, the frequency of the different traits you see in this population will change. And if they are drastic enough, maybe these guys start becoming dominant and start not liking these guys because they're so different or whatever else. We could see a lot of different reasons. This could eventually turn into... | Variation in a Species (2).mp3 |
This could eventually turn into a different species. Now, the obvious question is, what leads to this variation? In a population, what leads to this? In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin c... | Variation in a Species (2).mp3 |
In fact, even in our population, what leads to one person having dirty blonde hair, one person having brown hair, one person having black hair, and the spectrum of skin complexions and heights is pretty much infinite? What causes that? And then one thing that I kind of point to, and we talked about this a little bit in... | Variation in a Species (2).mp3 |
The DNA, we learned, is just a sequence of these bases. So adenine, guanine, let's say I got some thymine going, I have some more adenine, some cytosine. And that these code, if you have enough of these in a row, maybe you have a few hundred or a few thousands of these, these code for proteins or they code for things t... | Variation in a Species (2).mp3 |
But maybe you have a change in one of them. Maybe this cytosine, for whatever reason, becomes a guanine randomly. Or maybe these get deleted. And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without... | Variation in a Species (2).mp3 |
And that would change the DNA. But you can imagine, if I went to someone's computer code and just randomly started changing letters and randomly started inserting letters without really knowing what I'm doing, most of the time I'm going to break the computer program. Most of the time, the great majority of the time, th... | Variation in a Species (2).mp3 |
For example, if I go into someone's computer program and if I just add a couple of spaces or something, that might not change their computer program. But if I start getting rid of semicolons and start changing numbers and all that, it'll probably make the computer program break. So it'll either do nothing or it'll actu... | Variation in a Species (2).mp3 |
Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series of videos on cancer and that itself obviously would hurt the organism as a whole. Although if it occurs after the organism is reproduced, it might not be something that selects against the organism. But anyway, an... | Variation in a Species (2).mp3 |
But anyway, and it also wouldn't be passed on. But anyway, I won't go too detailed into that. But the whole point is that mutations don't seem to be a satisfying source of variation. They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the ... | Variation in a Species (2).mp3 |
They could be a source or kind of contribute on the margin, but there must be something more profound than mutations that's creating the diversity even within, or maybe I should call the variation, even within a population. And the answer here is really, it's kind of right in front of us. It really addresses kind of on... | Variation in a Species (2).mp3 |
And it's so fundamental that a lot of people never even question why it is the way it is. And that is sexual reproduction. And when I mean sexual reproduction, it's this notion that you have, and pretty much if you look at all organisms that have nucleuses, and we call those eukaryotes, maybe I'll do a whole video on e... | Variation in a Species (2).mp3 |
But it's the notion that if you look universally all the way from plants, not universally, but if you look at cells that have nucleuses, they almost universally have this phenomenon that you have males and you have females. In some organisms, an organism can be both a male and a female, but the common idea here is that... | Variation in a Species (2).mp3 |
Maybe other cells would just butt off from me, and then randomly one cell might be a little bit different and whatever else. But that would, as we already talked about, most of the time we would have very little change, very little variation. And whatever variation does occur because of any kind of noise being introduc... | Variation in a Species (2).mp3 |
Most of the times it'll break the organism. Now, when you have sexual reproduction, what happens? Well, you keep mixing and matching every possible combination of DNA in a species pool of DNA. Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me s... | Variation in a Species (2).mp3 |
Let me make this a little bit more concrete for you. So let me erase this horrible drawing I just did. So we all have, let me stick to humans because that's what we are. We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I... | Variation in a Species (2).mp3 |
We have 23 pairs of chromosomes, and in each pair we have one chromosome from our mother and one chromosome from our father. So let me draw that. So I'll do my father's chromosomes in blue, so I have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and I'm running out of space. Let me do more here. 16, 17, 18, 19, 20... | Variation in a Species (2).mp3 |
Let me do more here. 16, 17, 18, 19, 20, 21, 22. And then I'll throw another one here that looks a little bit different. I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a mo... | Variation in a Species (2).mp3 |
I'll throw one here that looks like a Y. And we'll talk more about the X's and the Y chromosomes. And I have 23 chromosomes from my mother. And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, ... | Variation in a Species (2).mp3 |
And not to be stereotypical, but maybe I'll do that in a more feminine color. Let's see. So I have 23 chromosomes from my mother. 1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father. | Variation in a Species (2).mp3 |
1, 2, I just have to draw 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23. So what's going on here? I have 23 from my mother. I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's s... | Variation in a Species (2).mp3 |
I have 23 from my father. Now, each of these chromosomes, and I made them right next to each other. So for example, let me zoom in on one pair of these. So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it th... | Variation in a Species (2).mp3 |
So let's say we look at chromosome number 3. So let me zoom in on chromosome number 3. I have one from my mother right here. And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it crea... | Variation in a Species (2).mp3 |
And remember, actually maybe I'll do it this way. Remember, a chromosome is just a big, if you take the DNA, it just keeps wrapping around. It actually wraps around all these proteins and it creates the structure. But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have million... | Variation in a Species (2).mp3 |
But it's just a big, you see it like that, you're like, oh, maybe the DNA, no, but this could have millions of base pairs. So maybe it'll look something like that. It's a densely wrapped version of, well, it's a long string of DNA, and when it's normally drawn like this, which is not always the way it is, and we'll tal... | Variation in a Species (2).mp3 |
So let's say that's from my mother and that's from my father. Now, these are both, we call them, I'll call them, they're the same, let's call this chromosome 3. They're both chromosome 3. And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross... | Variation in a Species (2).mp3 |
And what the idea is here is that I'm getting different traits from my father and from my mother. For example, and I'm doing a gross oversimplification here, but this is really to just give you the idea of what's going on. This chromosome 3, maybe it contains this trait for hair color. And maybe my father had, and I'll... | Variation in a Species (2).mp3 |
And maybe my father had, and I'll use my actual example, my father had very straight hair. So let's say he had, some place on this chromosome, there is a gene for hair straightness. Let's say it's a little thing right there. And remember, that gene could be thousands of base pairs. But let's say this is hair straightne... | Variation in a Species (2).mp3 |
And remember, that gene could be thousands of base pairs. But let's say this is hair straightness. So my father's version of that gene, or he had the allele for straightness. And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mo... | Variation in a Species (2).mp3 |
And remember, an allele is just a version of a gene. So I'll call it the allele straight for straight hair. Now, this other chromosome that my mother gave me, this essentially, and there are exceptions, but for the most part, it codes for the same genes. And that's why I put them next to each other. So this will also h... | Variation in a Species (2).mp3 |
And that's why I put them next to each other. So this will also have the gene for hair straightness or curliness. But my mom does happen to actually have curly hair. So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the... | Variation in a Species (2).mp3 |
So she has the gene right there for curly hair. So she has the version of the gene here is, let's see, allele curly. The gene just says, look, this is the gene for whether or not your hair is curly. Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and... | Variation in a Species (2).mp3 |
Each version of the gene is called an allele. Allele curly. Now, when I got both of these in my body, or in my cells, and this is in every cell of my body, every cell of my body except for, and we'll talk a little in a few seconds about my germ cells, but every cell other than the ones that I use for reproduction have ... | Variation in a Species (2).mp3 |
But only certain chromosomes are, for example, these genes will be completely useless in my fingernails because all of a sudden, the straight and the curly don't matter that much. And I'm simplifying. Maybe they will on some other dimension. But let's say for simplicity, they won't matter in certain places. So certain ... | Variation in a Species (2).mp3 |
But let's say for simplicity, they won't matter in certain places. So certain genes are expressed in certain parts of the body, but every one of your body cells, and we call those somatic cells, and we'll separate those from the sex cells or the germ cells that we'll talk about later. So this is my body cells. So this ... | Variation in a Species (2).mp3 |
So this is the great majority of your cells. And this is opposed to your germ cells. And the germ cells, I'll just write it here just so you get it clear, for a male, that's the sperm cells. And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give ... | Variation in a Species (2).mp3 |
And for a female, that's the egg cells or the ova. But most of my cells have a complete collection of these. What I want to give you the idea is that for every trait, I essentially have two versions, one from my mother and one from my father. Now these right here are called homologous chromosomes. Chromosomes, homologo... | Variation in a Species (2).mp3 |
Now these right here are called homologous chromosomes. Chromosomes, homologous. What that means is every time you see the prefix homologous, or if you see like homo sapien, or even the word homosexual or homogeneous, it means same. You see that all the time. So homologous means that they're almost the same. They're co... | Variation in a Species (2).mp3 |
You see that all the time. So homologous means that they're almost the same. They're coding for the most part the same set of genes, but they're not identical. They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotyp... | Variation in a Species (2).mp3 |
They actually might code for slightly different versions of the same gene. So depending on what versions I get, what is actually expressed for me. So my genotype, let me introduce another word. And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got l... | Variation in a Species (2).mp3 |
And I'm overwhelming you with words here. So my genotype is exactly what alleles I have, what versions of the gene. So I got like the fifth version of the curly allele. There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phe... | Variation in a Species (2).mp3 |
There could be multiple versions of the curly allele in our gene pool. And maybe I got some version of the straight allele. That is my genotype. My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much th... | Variation in a Species (2).mp3 |
My phenotype is what my hair really looks like. So for example, two people could have different genotypes with the same, but they might code for hair that looks pretty much the same. So it might have a very similar phenotype. So one phenotype can be represented by multiple genotypes. So that's just one thing to think a... | Variation in a Species (2).mp3 |
So one phenotype can be represented by multiple genotypes. So that's just one thing to think about. And we'll talk a lot about that in the future, but I just want to introduce you into that there. Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's g... | Variation in a Species (2).mp3 |
Now, I entered this whole discussion because I wanted to talk about variation. So how does variation happen? Well, what's going to happen when I, so first of all, well, let me put it this way. What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of... | Variation in a Species (2).mp3 |
What's going to happen when I reproduce and I have a son? Well, my contribution to my son is going to be a random collection of half of these genes. I'm going to contribute either one. For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let... | Variation in a Species (2).mp3 |
For each homologous pair, I'm either going to contribute the one that I got from my mother or the one that I got from my father. So let's say that the sperm cell that went on to fertilize my wife's egg, it just happened to have, let's say it happened to have that one, that one, well, I could just pick one from each of ... | Variation in a Species (2).mp3 |
Well, for every set, I can pick one of the two homologous chromosomes, and I'm going to do that 23 times. 2 times 2 times 2, so it's 2 to the 23rd. So there's 22 to the 23 different versions that I can contribute to any son or daughter that I might have. We'll talk about how that happens when we talk about meiosis or m... | Variation in a Species (2).mp3 |
We'll talk about how that happens when we talk about meiosis or mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of chromosomes in sperm, you only have 23 chromosomes. So for example, I'll take one from each of those, and through the process of meiosis, which we'll g... | Variation in a Species (2).mp3 |
And each sperm cell will have one from each of these pairs, one version from each of those pairs. So maybe for this chromosome, I get it from my dad. From the next chromosome, I get it from my mom. Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then... | Variation in a Species (2).mp3 |
Then I donate a couple more from, I shouldn't have drawn them next to each other, I donate a couple more from my mom, then for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 23rd combinations here, because there are 23 pairs that I'm collecting from. Now, my wife's egg is go... | Variation in a Species (2).mp3 |
There are 2 to the 23 different combinations of DNA that she can contribute, just based on which of the homologous pairs she will contribute. So the possible combinations that just one couple can produce, and I'm using my life as an example, but you could use this, this applies to everything. This applies to every spec... | Variation in a Species (2).mp3 |
So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of DNA, then we can produce 2 to the 46th combinations. Now, just to give an idea of how large of a number this is, this is 12,000, roughly 12,000 times the number of human beings on the planet today. So there's a huge amo... | Variation in a Species (2).mp3 |
And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and we'll talk about when this happens in meiosis, you can actually have DNA recombination. And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called cros... | Variation in a Species (2).mp3 |
And what you end up with after the crossover is that one DNA, the one that came from my mom, or that I thought came from my mom, now has a chunk that came from my dad. And the chunk that came from my dad now has a chunk that came from my mom. Let me do it in the right color. It came from my mom like that. And so that e... | Variation in a Species (2).mp3 |
It came from my mom like that. And so that even increases the amount of variety even more. So you can almost now, instead of talking about the different chromosomes that you're contributing, where the chromosomes are each of these collections of DNA, you can almost go to the different combinations at the gene level. An... | Variation in a Species (2).mp3 |
And now you can think about an almost infinite form of variation. And you can think about all of the variation that might emerge when you start mixing and mashing different versions of the same gene in a population. And you don't just look at one gene. I mean, the reality is that genes by themselves very seldom code fo... | Variation in a Species (2).mp3 |
I mean, the reality is that genes by themselves very seldom code for a specific. You can very seldom look for one gene and say, oh, that is brown hair. Or look for one gene and say, oh, that's intelligence. Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way... | Variation in a Species (2).mp3 |
Or that is how likable someone is. It's usually a whole set of genes interacting in an incredibly complicated way. Hair might be coded for by this whole set of genes on multiple chromosomes. And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the dif... | Variation in a Species (2).mp3 |
And this might be coded for a whole set of genes on multiple chromosomes. And so then you can start thinking about all of the different combinations. And then all of a sudden, maybe some combination that never existed before all of a sudden emerges. And that's very successful. But I'll leave you to think about it becau... | Variation in a Species (2).mp3 |
And that's very successful. But I'll leave you to think about it because maybe that combination might be passed on or it may not be passed on because of this recombination. But we'll talk more about that in the future. But I wanted to introduce this idea of sexual reproduction to you because this really is the main sou... | Variation in a Species (2).mp3 |
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