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But I wanted to introduce this idea of sexual reproduction to you because this really is the main source of variation within a population. And it's kind of a philosophical idea because we almost take the idea of having males and females for granted because it's this universal idea. But I did a little reading on it. It ... | Variation in a Species (2).mp3 |
It turns out that this actually only emerged about 1.4 billion years ago. That this is almost a useful trait because once you introduce this level of variation, the natural selection can start. You can kind of say that when you have this more powerful form of variation than just pure mutations, and maybe you might have... | Variation in a Species (2).mp3 |
But now that you have this sexual reproduction and you have this variation, natural selection can occur in a more efficient way so that species that were able to reproduce and essentially recombine their DNA and mix and match it in this way were able to produce more variety and were able to essentially be selected for ... | Variation in a Species (2).mp3 |
And it can be a pretty involved process, and even the way I'm going to do it, as messy as it looks, it's going to be cleaner than actually what goes on inside of your cells and other organism cells, because I'm going to show clearly from going from glucose and then see how we can produce ATP through glycolysis and the ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
We have a six-carbon chain right over here, and we have the process of glycolysis, which is occurring in the cytosol of our cells. So if this is the cell right over here, you can imagine, well, the glycolysis could be occurring right over there. And that process of glycolysis is essentially splitting up this six-carbon... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And in the process of doing so, and this is, I guess you could say, the point of glycolysis, we're able to, on a net basis, produce two ATPs. We actually produce four, but we have to use two. So on a net basis, we produce two ATPs, and I'm going to keep a little table here to keep track. So we produce two ATPs, and we ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So we produce two ATPs, and we are also, we're also in the process of that, we reduce two NAD molecules to NADH. Remember, reduction is gaining of electrons. And you see over here, this is positively charged, this is neutrally charged, it essentially gains a hydride. So this is reduction. And if we go all the way throu... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So this is reduction. And if we go all the way through the pathway, all the way to oxidative phosphorylation, the electron transport chain, these NADHs, the reduced form of NAD, they can be then oxidized to provide, and in doing so, more energy is provided to produce even more ATPs, but we'll get to that. So you're als... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Two NADHs get produced. Now at that point, you could kind of think of it as a little bit of a decision point. If there's no oxygen around, or if you're the type of organism that doesn't want to continue for some reason with cellular respiration or doesn't know how, this pyruvate can be used for fermentation. And we hav... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And we have videos on fermentation, lactic acid fermentation, alcohol fermentation. And fermentation is all about using the pyruvates to oxidize your NADH back into NAD so it can be reused again for glycolysis. So even though the NADH has energy that could be eventually converted to ATP, and even though the pyruvates h... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But let's assume we're not going to go down the fermentation pathway, and we're going to continue with traditional aerobic cellular respiration using oxygen. Well, the next thing that's going to happen is that the carboxyl group, and everything I'm going to show now, it's going to happen for each of these pyruvates. So... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So I'm going to multiply a bunch of things times two. But what happens in the next step is this carboxyl group, this carboxyl group is stripped off of the pyruvate and it essentially is going to be released as carbon dioxide. So this is our carbon dioxide being released here. And then the rest of our pyruvate, which is... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And then the rest of our pyruvate, which is essentially an acetyl group, that latches on to coenzyme A. And you'll hear a lot about coenzyme A. Sometimes they'll write just coA like this. Sometimes they'll do coA and then the sulfur bonded to the hydrogen. And the reason why they'll draw the sulfur part is because the ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Sometimes they'll do coA and then the sulfur bonded to the hydrogen. And the reason why they'll draw the sulfur part is because the sulfur is what bonds with the acetyl group right over here. So you have the carbon dioxide being released and then the acetyl group bonding with that sulfur. And by doing that you form ace... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And by doing that you form acetyl coA. And acetyl coA, just so you know, you only see three letters here, but this is actually a fairly involved molecule. This is actually a picture of acetyl coA. I know it's really small, but hopefully you appreciate it's a more involved molecule that the acetyl group that we're talki... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
I know it's really small, but hopefully you appreciate it's a more involved molecule that the acetyl group that we're talking about is just this part right over here. And it's a coenzyme. It's really acting to transfer that acetyl group. And we'll see that in a second. But it's also fun to look at these molecules becau... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And we'll see that in a second. But it's also fun to look at these molecules because once again we see these patterns over and over again in biology or biochemistry. So acetyl coA, you have an adenine right over here. It's hard to see, but you have a ribose and you also have two phosphate groups. So this end of the ace... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
It's hard to see, but you have a ribose and you also have two phosphate groups. So this end of the acetyl coA is essentially an ADP. But it's used as a coenzyme. Everything that I'm talking about, this is all going to be facilitated by enzymes and the enzymes will have cofactors, coenzymes, if we're talking about organ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Everything that I'm talking about, this is all going to be facilitated by enzymes and the enzymes will have cofactors, coenzymes, if we're talking about organic cofactors, that are going to help facilitate things along. And as we see, the acetyl group joins on to the coenzyme A, forming acetyl coA. But that's just a te... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
The acetyl coA is essentially going to transfer the acetyl group over to, and now we're going to enter into the citric acid cycle. It's going to transfer these two carbons over to oxaloacetic acid to form citric acid. So it's going to transfer these two carbons to this one, two, three, four carbon molecule to form a on... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Now before we go into the depths of the citric acid cycle, I want to make sure that I don't lose track of my accounting, because even that step right over here where we decarboxylated the pyruvate, we went from pyruvate to acetyl coA, that also reduced some NAD to NADH. Now this is going to happen once for each pyruvat... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So this is going to be times two. So we're going to produce two NADHs in this step going from pyruvate to acetyl coA. Now the bulk of, I guess you could say, the catabolism of the carbons or the things that are eventually going to produce our ATPs are going to happen in what we call the citric acid or the Krebs cycle. ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
It's called the citric acid cycle because when we transferred the acetyl group from the coenzyme A to the oxaloacetic acid, we formed citric acid. And citric acid, this is the thing that you have in lemons or orange juice. It is this molecule right over here. And the citric acid cycle, and it's also called the Krebs cy... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And the citric acid cycle, and it's also called the Krebs cycle, when you first learn it, it seems very, very complex, and some could argue that it is quite complex, but I'm just going to give you an overview of what's going on. The citric acid, once again, six carbon, it keeps getting broken down through multiple step... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So there's a bunch of cycles going on. But the important takeaway is as we go through the citric acid cycle, as we go from one intermediary to the next, we keep reducing NAD to NADH. In fact, we do this three times for each cycle of the citric acid cycle. But remember, we're going to do this for each acetyl-CoA, for ea... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
But remember, we're going to do this for each acetyl-CoA, for each pyruvate. So all of this stuff is going to happen twice. So we're going to go through it twice for each original glucose molecule. So here we have one, two, three NADHs being produced, but since we're going to go through it twice, and we're going to do ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So here we have one, two, three NADHs being produced, but since we're going to go through it twice, and we're going to do the accounting for the original glucose molecule, we could say that we have six NADs get reduced to NADH. Now you also, in the process, as you're breaking down, going from the six-carbon molecule to... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So we could also say that we're going to directly, remember we're going to do all of this stuff twice. So we could say that two, I'll just say two ATPs to make it simple. We could say GTP, but I'll say two ATPs, because once again, this happens once in each cycle, but we're going to do two cycles for each glucose. And ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And then we have this other coenzyme right over here, FAD. That gets reduced to FADH2, but that stays covalently attached to the enzymes that are facilitating it. So eventually that's being used to reduce coenzyme Q to QH2. So I'm just going to write the QH2 here, but once again you're going to get two of these. So two... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So I'm just going to write the QH2 here, but once again you're going to get two of these. So two QH2s. Now let's think about what the net product over here is going to be. And to think about it, we should just, I'll do a little bit of a shorthand, we'll go into more detail in future videos, is these coenzymes, the NADH... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And to think about it, we should just, I'll do a little bit of a shorthand, we'll go into more detail in future videos, is these coenzymes, the NADH, the QH2, these are going to be oxidized during oxidative phosphorylation and the electron transport chain to create a proton gradient across the inner membrane of mitocho... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
Each of the reduced coenzyme Qs, so the QH2, that's going to each produce about one and a half ATPs. And people are still getting a good handle on exactly how this is happening. It depends on the efficiency of the cell and what the cell is actually trying to do. So using these ranges, actually I'll say one and a half t... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So using these ranges, actually I'll say one and a half to two, one and a half to two ATPs, and these are approximate numbers. So let's think about what our total accounting is. So if we just count up the ATP or the GTPs, we're going to get two there and two there. So we're going to have four direct or very close to di... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
So we're going to have four direct or very close to direct ATPs, net being created. And then how many NADHs? We have two, four, and then we add six, we have 10 NADHs. And then we have two of the coenzyme Qs, two QH2s. So that's going to be four ATPs. This is going to be between 20 and 30 NADHs, sorry, 20 and 30 ATPs. A... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And then we have two of the coenzyme Qs, two QH2s. So that's going to be four ATPs. This is going to be between 20 and 30 NADHs, sorry, 20 and 30 ATPs. And then this is going to be three to four ATPs. So if you add them all together, if you add the low ends of the range, you get, let's see, 20 plus three plus four, tha... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And then this is going to be three to four ATPs. So if you add them all together, if you add the low ends of the range, you get, let's see, 20 plus three plus four, that's 27 ATPs. And the high end of the range, let's see, you have four plus 30 plus four, you have 38 ATPs. And 38 ATPs is currently considered to be kind... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
And 38 ATPs is currently considered to be kind of a theoretical maximum, but when we actually observe things in cells, it looks like it comes out at around 29 to 30 ATPs. And once again, it depends what the cell's trying to do, the type of cells and the type of efficiency. But all of this is happening through cellular ... | Overview of cellular respiration Cellular respiration Biology Khan Academy.mp3 |
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 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... | Variation in a Species.mp3 |
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 it makes maybe all of a sudd... | Variation in a Species.mp3 |
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 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 ... | Variation in a Species.mp3 |
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 different traits you see in this population will change. And if they are drastic enough, maybe these guys start be... | Variation in a Species.mp3 |
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 a different species. Now, the obvious question is, what leads to this variation? In a populatio... | Variation in a Species.mp3 |
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 complexions and heights is pretty much infinite? What ... | Variation in a Species.mp3 |
What causes that? And then one thing that I kind of point to, and we talked about this a little bit in the DNA video, is this notion of mutations. 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... | Variation in a Species.mp3 |
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 that control other proteins. But maybe you have a change ... | Variation in a Species.mp3 |
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 really knowing what I'm doing, most of the ... | Variation in a Species.mp3 |
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, this is going to go nowhere. For ... | Variation in a Species.mp3 |
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 actually kill the organisms most of the time. Mutations. Sometimes they might make the actual cell kind of go run amok and we'll do a whole maybe series o... | Variation in a Species.mp3 |
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, and it also w... | Variation in a Species.mp3 |
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 diversity even within, or maybe I should call t... | Variation in a Species.mp3 |
And the answer here is really, it's kind of right in front of us. It really addresses kind of one of the most fundamental things about biology. 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... | Variation in a Species.mp3 |
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 eukaryotes versus prokaryotes. But it's the notion that if you look universally all the way... | Variation in a Species.mp3 |
In some organisms, an organism can be both a male and a female, but the common idea here is that all organisms kind of produce versions of their genetic material that mix with other organisms' version of their genetic material. If mutations were the only source of variation, then I could just butt off other cells. Mayb... | Variation in a Species.mp3 |
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 introduced into this kind of butting process where I just replicate myself identically, most of the times it'll be negative. Most of ... | Variation in a Species.mp3 |
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 stick to humans because that's what we are. W... | Variation in a Species.mp3 |
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'll do my father's chromosomes in blue, so I have 1, ... | Variation in a Species.mp3 |
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, 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. An... | Variation in a Species.mp3 |
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 more feminine color. Le... | Variation in a Species.mp3 |
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, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 2... | Variation in a Species.mp3 |
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. Now, each of these chromosomes, and I made them right next to each other. | Variation in a Species.mp3 |
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 say we look at chromosome number 3. So let me zoom in on chromosome number 3. | Variation in a Species.mp3 |
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 this way. Remember, a chromo... | Variation in a Species.mp3 |
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 creates the structure. But it's just a big, you s... | Variation in a Species.mp3 |
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 millions of base pairs. So maybe it'll look something lik... | Variation in a Species.mp3 |
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 talk more about like that, they draw it as densely packed like that. So let's say that's from my mother and that's from my fat... | Variation in a Species.mp3 |
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 oversimplification here, but this is really to just give you ... | Variation in a Species.mp3 |
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 use my actual example, my father had very straight hair. So let's say he had, some place on this ... | Variation in a Species.mp3 |
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 straightness. So my father's version of that gene, or he had the allele for straightness. And remembe... | Variation in a Species.mp3 |
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 mother gave me, this essentially, and there are exceptions, ... | Variation in a Species.mp3 |
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 have the gene for hair straightness or curliness. But ... | Variation in a Species.mp3 |
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 gene for whether or not your hair is curly. E... | Variation in a Species.mp3 |
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 this is in every cell of my body, every cell of... | Variation in a Species.mp3 |
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 this complete set of chromosomes in it, which ... | Variation in a Species.mp3 |
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 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 t... | Variation in a Species.mp3 |
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 is the great majority of your cells. And this is opposed to your ge... | Variation in a Species.mp3 |
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 you the idea is that for every trait, I essen... | Variation in a Species.mp3 |
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, homologous. What that means is every time you see the prefi... | Variation in a Species.mp3 |
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 coding for the most part the same set of genes, but they'r... | Variation in a Species.mp3 |
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 genotype, let me introduce another... | Variation in a Species.mp3 |
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 like the fifth version of the curly allele. There could be multiple versions... | Variation in a Species.mp3 |
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 phenotype is what my hair really looks like. ... | Variation in a Species.mp3 |
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 the same. So it might have a very similar phenotype. So one phenotype can... | Variation in a Species.mp3 |
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 about. And we'll talk a lot about that in the fut... | Variation in a Species.mp3 |
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 going to happen when I, so first of all, well, let me put it... | Variation in a Species.mp3 |
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 half of these genes. I'm going to contribute either one. For each homologous p... | Variation in a Species.mp3 |
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's say that the sperm cell that went on to fertilize my wi... | Variation in a Species.mp3 |
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 these 23 sets. And you could say, well, how many combinations are there? Well, for every set, I can pick one of the two homologou... | Variation in a Species.mp3 |
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 mitosis. That when I generate my sperm cells, sperm cells are essentially, instead of having 23 pairs of ch... | Variation in a Species.mp3 |
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 go into, I'll generate a bunch of sperm cells. And each sperm cell will ha... | Variation in a Species.mp3 |
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 for the chromosome number 5, it comes from my dad, and so on and so forth. But there's 2 to the 2... | Variation in a Species.mp3 |
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 going to have the same situation. 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 combinat... | Variation in a Species.mp3 |
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 species that experiences sexual reproduction. So if I can give 2 to the 23rd combinations of DNA, and my wife can give 2 to the 23 combinations of... | Variation in a Species.mp3 |
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 amount of variation that even one couple can produce. And if you thought that even that isn't enough, it turns out that amongst these homologous pairs, and w... | Variation in a Species.mp3 |
And all that means is that when these homologous pairs during meiosis line up near each other, you can have this thing called crossover, where all of this DNA here crosses over and touches over here, and all of this DNA crosses over and touches over there. So all of this goes there, and all of this goes there. And what... | Variation in a Species.mp3 |
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 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... | Variation in a Species.mp3 |
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. And now you can think about an al... | Variation in a Species.mp3 |
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 for a specific. You can very seldom look for one gene and say, oh, t... | Variation in a Species.mp3 |
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. Hair might be coded for by this whole set of genes on multiple chromosomes. And... | Variation in a Species.mp3 |
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 different combinations. And then all o... | Variation in a Species.mp3 |
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 because maybe that combination might be passed on or it may not be passed on be... | Variation in a Species.mp3 |
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