Genetic Drift

by Jason Amores Sumpter
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genetic drift is another way that we can get changes in Lille frequencies, and it's due to what's called random sampling. But basically the idea is that some a leal's get lucky in terms of the numbers. So we looked at when we talked about Mandelli in genetics. We looked at the, uh, the probabilities of Lille distributions from parents to offspring, and we saw that probability dictates that certain Leal's will be distributed at certain frequencies. But but that doesn't always happen. Just because there is a probability that it will occur doesn't necessarily mean that it will occur. And that's where randomness comes into play. So you can see here that we have a nice 50 50 mix of blue and red marbles. But over the generations are red. Marbles are more or less disappearing due to random sampling, and that is how genetic drift works. Basically, some wheels get lucky and others get unlucky, and we have a shift in Lille frequencies because our illegal distributions are not following those probability rules. Now the founder effect is when a small group from the population splinters off and forms a new one, taking a random sample of a Leal's with it. So you see, here in our starting population there's a relatively even number of of green and red dots. But our founding population doesn't have that same distribution. And in fact, over time we see that our founding population winds up with different alil and genotype frequencies than our original population. And that's due to the founder effect. The fact that these guys all left the group taking a random sample of Leal's that was not necessarily reflective of this larger populations, Alil frequencies and therefore their new population will show different illegal frequencies. With last type of genetic variation we're going to talk about is the bottleneck effect. And this is when population size dramatically decreases due to some random event, and this drastically alters alil frequencies so you can see and you take myself out of the image. Here. You can see a nice chart of population size over time and right here that's where we have this bottleneck event, which causes our population to plummet, and either it's going to go extinct or recover, and assuming it recovers well, when it recovers, it might wind up having you might wind up with a population of equal size and totally different legal frequencies because of the bottle necking. So you can see here we have a wide distribution of a Leal's. We have yellow, red, blue, green and pink. But our bottle necking event leaves us with mostly red, little blue and a little green. We don't have any more pink or yellow in the mix anymore. And that means if our population recovers, the illegal frequencies are going to look quite different than the initial population. That's all I have for this video on genetic variation and selection. I'll see you guys next time.