[Music] hi it's Mr Anderson and welcome to biology Essentials video number three this is on genetic drift or random evolutionary change um what I'm going to talk about in here is how we can get changes in a gene pool and so this right here represents a gene pool and and then these represent the alals inside that gene pool and so let me start it going for just a second and so um inside here we've got the original population uh if you weren't paying attention I could write some of the stuff out so we had a P value and a q value uh P value is the alal frequency of the dominant in this case let's say the dominant is red um and the Q value is going to be the recessive and so on the first time we've got um 10 and 10 and so our P value is going to be 0.5 and our Q value is going to be 0.5 so that'd be in the first generation now we randomly choose or we have sex from from that original population to create the second generation or we get this remixing of the genes and you can see in the second one that our alal frequency has dropped quite a bit it's now uh of the dominant we have3 and of the recessive we have 7 on the next one it even drops more now what's making it drop is simply chance so now it's 0.15 and .85 and now it goes to 2 and uh8 and then event eventually it goes to zero and 1.0 and so what we've seen is a drift or just due to random uh size of the population we get the elimination of that red Al or that red um color and that's genetic drift um if we were to graph that out and we were to put um the P value here at 0 five and 0.5 and I were to graph that let's get it in the right color the P value went from 0.5 down to. 3 down to uh 0.15 and then up to0 two and then eventually it dropped down to zero so this would be zero here and then if I do the blue color um the blue color went all the way to 1.0 and kind of mirrored that so it went like this went like that went like that and then eventually it went like that um and so when we graph those alal frequencies over time what we would find is that um the values would tend to drift in other words just due to random chance those alal frequencies are going to change like that or move in in different directions and so let me give you some actual data uh based on that let's look here on the internet and so this is a simulator it's a population simulator and so what I can do is I can actually have it do the coin flips inside it and so we're going to start with a population of 50 right now and if I just let it run you'll see that there's going to be random dri drifting and so we can think of this as the P value and this as the Q value and you can see that it eventually uh eliminated over time now let's try to increase the number though so let's say we go from 50 to 500 and we reset the population this time you'll see that there's actually less drift and the reason why we still get a little bit of drift in here is that you have a law of large numbers taking over and so it's less likely to get that changed just due to chance well let's really make the number large let's make it like 5,000 000 and if I click on go you can see it's going to take a lot longer for my computer to actually do this um because it takes a while to do all those coin flips but you can see that there's very little drift and so one of the things that's going to keep a a a Le um or a gene pool the same is going to be the the law of large numbers so let me talk about what I'm going to talk about um so in this uh we know that the gene pool is should remain at equilibrium and if we ever change our gene pool we call that solution and so in the first two podcasts I talk about natural selection and how natural selection can cause changes in the gene pool in this one I'm dealing with more of these ones up here these things that are based more on random chance because random chance has a lot to do with natural selection as well and the big thing I'm talking about is the size and so if we decrease the size then genetic drift starts to take over so for example let's say we have a population right here and then we have a smaller population that breaks off of that maybe they are birds that are blown to an island now Chance is going to take over and so these two populations are going to start to vary two real world examples of genetic drift are the bottleneck effect uh bottleneck effect is when you have a large population and that large population kind of gets squeezed through a bottleneck in other words the population's going to get smaller even though the population May recover on the other side of that bottleneck there are going to be huge implications as a result of losing all that genetic diversity an example I'll talk about is the uh almost extinction of the northern elephant seal and that's a human cause uh the next thing I want to talk about is the founder effect uh founder effect is similar but essentially it is one founding population making up the the forming population so I'm going to talk about an island in the Pacific called pingelap where a founding population made some huge uh changes in the uh phenotypes of The Offspring that came from that so this would be genetic drift for a population of 20 as we increase the size you'll see that less of that is going to be the change and so when we talk about an isolated population we could say that this here represents a gene pool and then all of these colors inside it are going to be the alals and maybe it starts with a 50/50 uh frequency to start with but once you break off and have smaller isolated populations from that chance can just take over and so you could have the elimination just due to chance not newe to adaptation at all and so example of where this might play out let's say this is a population of tortoises that float to an island um they're exactly the same as the tortoises on the mainland but due to just random chance you're going to get changes to the point where this actually becomes a new species now there could be adaptation here as well but just chance in itself has huge implications when it comes to populations let me give you a couple of real world examples of the bottleneck effect uh and the and the founder effect uh bottleneck effect remember occurs when the population gets squeezed through a small bottleneck so these are elephant seals elephant seals were hunted almost to Extinction the northern elephant seal live along the west coast of the US down through into Mexico and their population had dropped down to some scientists think maybe dropped down to the point of there were just 50 left on one Island in Mexico and so this is in the 1800s and so their population was squeezed through a huge bottleneck um if you look at the southern elephant seal the Souther Southern elephant seal lives in way down here by Antartica and didn't see that pressure um they look very similar they just live in different areas so they're very closely related but some scientists and you can see the citation right here some scientists took a look at the bottleneck effect and what effect it had on the northern elephant seal its population remember had gone from uh a few hundred thousand down to 50 and then had gone up to I think now it's over 150,000 left so it had been squeezed through this tiny bottleneck and so what they did is they actually looked at elephant seals before the bottleneck and after the bottleneck to see how they were affected now you might think to yourself how could we do that how could we look at them before they actually went extinct which if it was in the 1800s well what they did is they grabbed a number of skulls from the Smithsonian so they've got about 11 skulls pre- bottleneck and then they were able to extract DNA and so in this case what they did is they looked at the DNA they looked at mitochondrial DNA that's the first thing they did in their study and what they found is that they had lost a huge amount of genetic diversity in other words when they looked at these pre- bottleneck northern elephant seal DNA there was a huge amount of diversity but after the bottleneck they're very very similar the second thing they looked at was they wanted to look at symmetry they wanted to see if that actually can affect the skull itself can it affect what they like can it make them less fit phenotypically and so what they did here to kind of put out the data is that they had um here's Southern elephant seal um here's pre- bottleneck northern elephant seal and then here's post bottleneck northern elephant seal and what they were doing was looking at symmetry symmetry of the skull does the right side look like the left side and so they measured this value right here on the lower mandible and they graphed the left mandible distance versus the right mandible distance and you can see that the southern elephant seals there's a really nice linear relationship they then did the same thing with these old skulls from the Smithsonian and they found that there's a linear relationship as well and you can see the r values are close to one which means it's really close to a linear relationship but then they looked at the SYM of the post um bottleneck northern elephant seal and they find that the data is all over the place in other words their skull is very um asymmetrical what does that mean well when you decrease the DNA you're actually having it's manifesting itself on the morphology or the outward appearance of the skull and so that could make them less fit to changes in the environment or more susceptible to uh another Extinction or another bottlenecking effect another example related to humans would be the founder effect so the founder effect um can happen in any organisms but the founder effect is when you have a small population that finds a new area or is the founding population of that new area and so I didn't know about this but maybe you did in the uh in the South Pacific we have What's called the Federated States of Micronesia and in there is a tiny little island called pingelap um and it was doing well back in the day but in the 1700s they had a massive uh typhoon and that typhoon swept through pingelap and as it did that it killed almost everybody on the island so their population dropped down to around 20 so those 20 people were the new founding population of pingelap and all the people who live there today are are uh descendants of that first 20 people now what's interesting is that the leader of pingelap uh I'm not going to try to pronounce his name but the leader of pingelap uh one of these 20 survivors actually had an odd form of colorblindness where he had complete color blindness um in other words when he looked at a a maau like this he sees it in Gray scale couldn't see any color at all this is really rare something like one in every 33,000 people in the United States have this but since this was the founding population very quickly 5% of the people and now I think the numers up to around 10% of the people on pingelap have um complete color blindness and that's due to just the random chance in that founding population now the number is going higher than it was originally and so that suggests that there's inbreeding as well and if this is the leader of that population there could have been quite a bit of inbreeding as well and so that's an example of a founding effect it's just the chance of who happens to survive or who happens to land on that island or in that one area that can create huge repercussions for the uh for the rest of the the time of that uh population and so that's a genetic drift again it's just Randomness but it gets bigger and bigger and bigger the smaller the population is I hope that's helpful