Sometimes there may be a population that's very large, but it has surprisingly little genetic variation. Now remember, genetic drift can cause the loss of genetic variation as alleles are lost through just random change, but genetic drift has its greatest effect on small populations. So here we're going to look at special cases of genetic drift, and specifically, two particular situations that can result in accelerated genetic drift even in populations that end up being large. Alright. We're going to look at the founder effect and population bottleneck.
We'll start by looking at the founder effect here. In the founder effect, we're going to say a small subset of a population forms or founds a new population. Alright. So when that population is founded by just a few new individuals, well, that new population has allele frequencies matching the founders. Right?
So in our example here, we have this field of flowers, and you can see there are pink, white, and red flowers there. And we have allele frequencies, p equals 0.5, q equals 0.5 are 2 alleles here that we're looking at. There's an equal number in this population. But we have a barrier here, and it looks like just a couple of seeds were able to cross that barrier, and some new flowers are founding this new population. But just by chance, they're red flowers.
And our new allele frequency in this new population, well p equals 1. There's only one allele that made it across to this new population. In other words, that one allele has gone to fixation in this new population. And the other allele, well q equals 0, that other allele has been lost. Well, as these flowers, they're going to reproduce, and they're going to, you know, spread out, and that population might get very big in this new environment.
But the genetic variation, it's been lost already. Right? We've had this massive change in allele frequency because that population got very small. Those very that very small founding group didn't carry a lot of genetic variation with it. Alright.
So our other example here, kind of a related example, is population bottleneck. And a population bottleneck is when a sudden change to the environment reduces population size that later rebounds. Alright. So if you have a big population size, if that population crashes and gets very small for a little while and then gets big again, well, that's a population bottleneck. And when it was small, you're going to have that accelerated genetic drift because genetic drift happens the most in small populations.
So in that case, genetic drift is accelerated even though population size, again, is going to be large in the end. Alright. Now in this example, well, we have a field of flowers. Alright. The same field of flowers, same allele frequencies, p equals 0.5, q equals 0.5.
But here, well, we're showing in this case a fire. It could be different things that cause this, but in this case, a fire comes through, burns up, kills most of the plants except for just a few random ones there. And then those rare survivors, they reproduce. They sort of, you know, fill in the environment. They repopulate, but now our allele frequency has changed drastically.
Now p equals 0.18, q equals 0.82. You can imagine, you know, just as we looked at in founder effect, how alleles could be lost in this situation. And again, it was just a random effect by which organisms survived this environmental effect when the population got very small. Alright, so for both of these, the thing to take away, right, populations may be big, but what's most important for genetic drift is how small did they get at some point in time? Alright.
We'll look at this more and examples and practice to come. It'll be fun. I'll see you there.