This example tells me that a population has the following allele and genotype frequencies for the r gene. We are to assume that this population is not in Hardy-Weinberg equilibrium due to the presence of natural selection. Then we want to know what type of selection may be happening, and how do you know? Alright. So we have these allele frequencies, p equals 0.4 and q equals 0.6.
And we have our genotype frequencies, but we know that they're not in Hardy-Weinberg. So how could we figure this out? Well, we could compare them to what we would expect if it were in Hardy-Weinberg. So I'm going to do that. Right?
So the big RR genotype, well, that if it were in Hardy-Weinberg, that would be equal to p2, which is equal to 0.42, which equals 0.16. Alright. So it's actually pretty close, but there are looks like there's fewer of these bigger homozygotes in the population than I would expect if it were in Hardy-Weinberg. Well, how do I figure out the heterozygote? Well, I can go to pq is what that should equal if it's in Hardy-Weinberg.
So that's 2 times 0.4 times 0.6, which equals well, 2.4 times 0.6 is 0.24 times 2 is 0.48. Alright? So there's more heterozygotes than I would expect. And then what about my little rr? Well, you can probably see where this is going.
I'm going to take q2, and that equals 0.62, and that equals 0.36. Alright. So as I look at this, there are fewer of both homozygotes, despite a little bit, but there are fewer of each homozygotes than I would otherwise expect if it were in Hardy-Weinberg, and there's an excess of heterozygotes. Well, when I see that and it's due to natural selection, what do we call it? That's heterozygote advantage.
Right? So what would be happening in a population like this is it were otherwise in Hardy-Weinberg equilibrium. Each generation would start in Hardy-Weinberg, but then those homozygotes are not surviving at a higher rate. The heterozygotes are surviving more. And so the frequency of them, while they become more frequent in the population as those 2 homozygotes, well, as they die off.
All right. So how do I know this? I'm just going to say there's an excess of heterozygotes compared to homozygotes. When compared, I'm not going to write it all out, but if I'm being complete, I should say when compared to the Hardy-Weinberg expectation. Alright.
With that, more practice after this. Give it a try.