To wrap things up, we have this review table here, and we want to go through and just try to tie a lot of these ideas together and what we're calling putting it all together. Alright? So we're going to start by talking about Hardy Weinberg, and we said that the Hardy Weinberg principle says that the genotype frequency of a population will equal what's in this blue box here. Right? We can predict genotype frequencies, and we said that those big A big A homozygotes, we can predict using p squared.
We can predict the frequency of the heterozygotes using 2pq. We can predict the frequency of the little A homozygotes using q squared. We define p as the frequency of the big A allele or the first allele in our population. We define q as the frequency of the little A allele or that second allele in our population. And because, for our examples, we're always looking at genes with 2 alleles, p plus q is going to equal 1, because that's all the alleles in our population, or you could say in our gene pool.
Now from all that, we get the Hardy Weinberg equation here, where we can say that the equation p2 + 2pq + q2 is going to equal 1. Because, well, if we have only 2 alleles in the population, that's all the possible genotypes we could have in the population as well. Now with these two equations, we saw how we could solve different types of problems. Right? We can predict genotype frequencies from allele frequencies.
We can predict allele frequencies from genotype frequencies. We saw how we could test if actual populations were in Hardy Weinberg equilibrium. And I also said that I just kind of find this a profound idea. Right? We can make predictions about entire populations just knowing a little bit about allele frequencies, and it really opens up this idea to population genetics, where we make these really big predictions about whole populations.
Now that's very different from Mendelian genetics or classical genetics, where we're usually just looking at the inheritance of alleles through single matings. Alright. But we said populations actually often aren't in Hardy Weinberg equilibrium because we have some assumptions. And if those assumptions are broken, it's probably going to push that population a little away from that perfect Hardy Weinberg expectation. So the reasons a population may not be in a Hardy Weinberg, that's what we're going to fill in in this table.
But first, let's remember our assumptions, and we had this memory tool for that. Remember we said, mating mutants? It's natural in flowers, and we have this kind of funny image here of these weird flowers kissing to remind us of that. So let's go through what these assumptions are. Remember, if any one of these assumptions is broken, it should push population out of Hardy Weinberg.
So mating, we need to assume random mating. Mutants, we have to assume no mutation. Natural, we need to assume no natural selection. In, we need to assume infinite population size or at least a very large population size. And that flow, that first part of flowers, we need to assume no gene flow.
Alright. So now let's go through this table. And in this table on the left, well, it says process. And that process is, you know, what's happening if one of those assumptions is broken. We're going to define what occurs when that is happening.
We're going to say, does genetic variation increase or decrease? We're going to use an up or down arrow to say that. And then for many of these, we sort of talked about special types, and we'll remind ourselves of those. Alright. So first, let's talk about non-random mating.
Non-random mating occurs when certain genotypes are more likely to mate with each other. And we said that is going to affect genotype frequency, and in that way, it's going to push that population out of Hardy Weinberg. But importantly, we said it does not affect allele frequency, and that's important because a change in allele frequency, we said is our measure of evolution. So remember, non-random mating does push a population out of Hardy Weinberg, but it doesn't cause evolution on its own. Now for genetic variation, I said, well, mark this with an up or down arrow.
I'm actually going to put a sideways arrow here because, well, again, we're just pairing alleles in a non-random way. We're not
