 So allele frequency is basically the composition of alleles in a population. So this visual, I love, because first of all, it has a bunch of warthogs. I love warthogs. Second of all, it has like a real little pool there. So it's got a very nice visual of all these warthogs with their alleles that are being dumped into the pool. And this pool, very lovely, represents the gene pool. The allele frequency is just basically the percentage of alleles in your gene pool, which is all the alleles in the population. What percentage of those are the allele you're interested in, such as little b, we could totally count them up. We could count up, look, how many total warthogs there are, how many little b alleles there are of all the warthog alleles, and then we could calculate the percentage of little b alleles and the percentage of big b alleles. That's the allele frequency in a population. Now, I'm going to show you how we're going to do that. We're going to have a little example and we're actually going to calculate it. Before we do that, I want you to remember that why are we talking about a population and what is this population that we speak of? Well, I want you to be really clear about the fact that the population, sometimes we refer to that as actually a species there. So sometimes we could call it a species, but species is really hard to define. For example, if you look at these two metal arcs, does anybody on the planet think that those are two different species? Like you look at those things, I look at those things and I love birds, but I look at them and I'm like, yes, sorry, those are exactly the same species. And whatever it is, I actually don't know why they distinguished that these or decided that these were two different species. Usually a species is defined as a group of critters that can make babies with each other. We're going to talk about that more in the next lecture. For whatever reason, they concluded that these guys, nope, they are not the same species. They don't make babies with each other. Why? There could be lots of reasons. But then take a look at these guys. Okay, clearly they are two different species of ants. Guess what? Not so. This is a big boy ant. This is the little boy ant. They're the same species. Like they could have had the same mom and dad. They're the same species of ant, but they just have super distinctive phenotypes to go with their very unique jobs that they have. The point is that sometimes determining what makes a species becomes really difficult. We talked about in lecture mules, donkeys, horses, and hinnies. And that mules and horses, donkeys and horses are two separate species, but they can make babies. The babies just can't make babies. But then you look at something like a lion and a tiger, and clearly we're like no dog pounds. Those are two different species. But if you throw them into a cage together, and you trap them behind bars, life gets tough. They'll actually make babies with each other. Crazy talk. So bottom line, if the critters are living together and they have a gene pool, then let's call them a population, and that's great. That's what we're going to focus on. The number of alleles in our gene pool. Okay, so let's calculate some allele frequencies. Now, here's our example. And let me tell you about it. Our example is going to be for tongue rolling. Can you do it? Are you cool? Are you a roller? Remember, rollers are... the tongue rolling trait is coded for by the dominant rolling allele. So rollers have at least one dominant allele. And non-rollers have to have two recessive alleles. So they're going to be homozygous recessive. Now, we're going to calculate the allele frequency. Oops, goodness. Allele frequency in my house. So I'm going to tell you right now that I have one small human who cannot roll his tongue. This is my child. So he has two little R's. I know that. Right away. I know that he's mine. He was in there. I pushed him out. Therefore, I know that I have to have at least one little R allele. And guess what? Yes, I can roll my tongue, which means I also have to have one dominant allele. Now, this small child's father can also roll his tongue. And so therefore, he has to have at least one dominant rolling allele. And he had to have a recessive allele to donate to my little non-roller. And then, just for the heck of it, for the heck of it, my other child is a roller, but he really is. That's not the heck of it part. The further heck of it part is that I'm going to say he could be homozygous dominant, in which case all of his kids, whoa, my kid's going to have kids, and then I'm going to be a grandma. What? Dude, there's no reason to start thinking that way right now. Settle down out there. When he has his kids, if he has any non-rollers, we'll know he's heterozygous. If he has 50 kids and they're all rollers, then we'll know he is homozygous dominant. I mean, I think that's fair game, don't you? I mean, come on, kai-kai, let's do a little genetic experiment, son. All right, so let's calculate our allele frequency. Are you ready? First of all, we got to know, how many little R alleles do we have in this population? You literally count alleles. One, two, three, four, five. We have five little R's. And we know that we have one, two, three, three big R's. Now, if we want to know a percentage, how many total alleles do we have in our gene pool? Okay, I can't help it. We got to have a pool. Here's our gene pool. How many total alleles are in our gene pool? Eight. If there's eight total alleles, I'm amazing. I did this math earlier. That means we have 62, oops, it's 62.5% of all the alleles in the population are little R. And that means that it is 37.5% of all the alleles in the population are big R. That's my allele frequency. Are you cool with the idea that if evolution is going to happen in this little population, it's the only thing that has to happen is that my allele frequency has to change. The consequences of allele frequencies changing can be vast. We can end up with whales and boys because allele frequencies change in populations. But how and why and what was the dead white guy who enlightened us in this regard? Well, it was old boy Darwin. I know y'all have heard of Darwin. So, take a look at how did he figure out? What did he figure out? He ultimately changing allele frequency is the mechanism. That is the power that causes variation in different populations and possibly speciation and big changes. But how? How does that work? Why would changes happen in the population? Like, look at this little population. Why would it ever change from this allele frequency? Let's go find out.