22. Evolutionary Genetics
Overview of Evolution
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Hi in this video, we're gonna be talking about an overview of evolution. So evolution is this process through which variation and individuals. So different thematic variation makes them more likely to survive and reproduce. And so there are three principles to how this happens. The first is that variation. So individuals within a population have some type of variation. And I think we would all agree that this is true. We see it in humans, not everyone is the same. We see it in birds, not every bird is the same. We see it in every organism on earth that there's variation that exists in that population. So that's the first principle. The second is heredity and that is that offspring resemble their parents more than they resemble unrelated individuals. So that is because genes are passed onto the offspring. So that variation can be passed on to the offspring. Everyone I think will agree with this. And then third is selection And that is that some variations of some of these forms, specific variation is more successful at surviving and therefore reproducing than other forms. So it's the variation that exists that we all see. Some of it all is inherited in the offspring. And some of that variation allows for those particular individuals and then their offspring to be more apt to survive in the condition at the time. So here is an example of Darwin's finches that he studied. We can definitely see variation and beak size, maybe a nice eyes and head size. Um If we were to look at the offspring of these finches, we would see that those offspring, the offspring of number one is going to resemble number one more than it would resemble 23 or four. And then finally selection um this variation potentially for number one because it has a bigger beak, it's able to break maybe harder nuts or seeds in order to get that food. So potentially it could survive more. And that would be an example of selection. It's really just what evolution is its variation that's inherited and then selected for. Now there's a theory of evolution that is the neutral theory. And this states that evolution isn't necessarily caused by one mutation that's been that's very positive and leads to this huge increase in fitness and survival and reproduction. But instead that most evolution is caused by genetic drift of neutral mutations. So you may say, okay, let me let me think about this. What is genetic drift? Remember genetic drift Is that random? Just passing on of random alleles of these different alleles in the population, it can lead to fixation, it can be lost. But essentially it's just the random selection of alleles that are passed onto the offspring. Because the number of offspring produced isn't infinite. So the number of offspring only has a selection of the in the gene pool. That's genetic drift. But a genetic drift of neutral mutations, neutral mutations are mutations that have no effect on the amino acid. So these are also called synonymous mutations and this can change one code onto an alternate code on and therefore there's no change in the amino acid produced and therefore no change in the protein that's made. However, a mutation was there. And so how and then the opposite of that is the non synonymous mutation which causes a change in amino acid. Now I think we would all agree that the majority of the mutations that happen in an organism are neutral, right there? Mostly happening in n tron they're not affecting the protein because most of the time if you're affecting the protein it's harming it and therefore it leads to death of the organism and therefore it's not selected for that spring isn't produced. And so the majority of the mutations that are created are neutral and therefore the majority of evolution that takes place happens because genetic drift randomly, selects for these neutral mutations just kind of randomly and that can lead to divergence of different species and evolution of the organism as a whole. Now there's two ideas of how different types of mutations, both neutral and then positive or negative mutations that occur can lead to evolution. The first is single step and that means that there's a single step. So there's one mutation, multiple mutations. This random mutation and it just happens all at once and that causes this selection for that trait, it's beneficial, it allows it to retain in the environment and it all happens in a single step, cumulative selection is different and that multiple single steps are accumulated over time and that leads the selection for the trait. So the best way to explain this is using the infinite monkey hypothesis and what this says and you've probably heard about it before right, is that if you set a monkey down at a typewriter, it's kind of an old hypothesis typewriters, but you set a monkey down at a typewriter and you just let them push random buttons for an infinite amount of time. Eventually at least one of those times the monkey would write the complete works of William Shakespeare and it's just by chance, right? If you let the monkey type every single sit there for so long that it can type every single combination of letters just randomly, at least one of them is going to be William Shakespeare's works just by random. So if we look at this and compare it to evolution, single step selection says that okay, well if the monkey is typing one of those times it'll happen at once and the monkey will if we let it sit there long enough, it's huge. I mean incredibly long amount of time. The monkey will just in one time write the single the single work of William Shakespeare, Cumulative selection for evolution says that okay, well we think that maybe takes too long to just wait for that monkey to just randomly do that in one single step. So what we're gonna have the monkey do is instead we're going to set the monkey down and we're gonna let it right 50 works that are as long as well Shakespeare. Once it's written 50 we're gonna have someone come in and pick which one is the best the best represents. William Shakespeare's work. Then when we have that best one, so this is the process of selection. So we have all these different organisms that are made and selection chooses that best one. Then the monkeys given that best one and allowed to improve on it to make it more like William Shakespeare. And it does this over multiple times that are accumulated. So each round 50 are tight and then somebody comes in and chooses the best one so that somebody comes in and choosing it. That's natural selection coming in and choosing which one is most like William Shakespeare. Which organisms more likely to survive. Then you do that for one round two. Round three rounds, four rounds, 10 rounds, 50 rounds. And it starts looking more and more like William Shakespeare. Even though it's the same process that's happening every time. So finally, at the end of however many rounds it takes 70 rounds, 100 rounds, 1000 rounds. That you do get this work of William Shakespeare. But it takes much less time because natural selection is coming in and selecting for in each round which one is the best or which organism is going to survive the best. Whereas in single step selection it all just if you wait long. enough it'll happen right. If you wait long enough for that monkey to type one at least one time. It'll be the random works of William Shakespeare. But it's gonna take a long time to let that monkey try all the different combinations that it can before it types that work. Whereas cumulative selection, natural selection is coming in. It's sort of selecting each round or each generation which one is the best and that eventually will lead to the complete works of William Shakespeare in a much less time consuming manner. So those are really the two main ideas. Um Obviously a lot of people prefer a cumulative selection but there is some evidence that, you know, the single step selections do and can happen as well with not just that one is right and one is wrong but that they're both acting to promote evolution. So with that let's move on.
The neutral theory of evolution states that which of the following is most responsible for evolution?
Allele creation through mutation
Which of the following is not one of the three main principles of evolution?
Additional resources for Overview of Evolution
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