The original source of new alleles, upon which selection operates, is mutation, a random event that occurs without regard to selectional value in the organism. Although many model organisms have been used to study mutational events in populations, some investigators have developed abiotic molecular models. Soll et al. (2006. Genetics 175: 267-275) examined one such model to study the relationship between both deleterious and advantageous mutations and population size in a ligase molecule composed of RNA (a ribozyme). Soll found that the smaller the population of molecules, the more likely it was that not only deleterious mutations but also advantageous mutations would disappear. Why would population size influence the survival of both types of mutations (deleterious and advantageous) in populations?

Question

Accepted Answer

Everybody. Let's look at our next problem. It says adaptive evolution is the evolutionary changes in an organism that make it suitable for its habitat. The main two factors that influence adaptive mutations include the rate of mutation and the population size based on population size. Rapid adaptive mutations will occur because and the other choices, we have to look at our choice, a larger populations produce more mutant individuals and experience more natural selection choice. B smaller populations experience no colonial interference and stronger genetic drift. Then see both A and B and D, none of these. So let's evaluate A and B keeping in mind that we could have a possibility that both are correct or neither is correct. So A let's start with a larger populations produce more mutant individuals. Um Well, this is correct. The larger the population, the more mutations will occur within that larger population as compared to a smaller one. So this is part is correct, doesn't experience more natural selection. Well, the more different mutations there, the more those mutations give material for natural selection to find some mutations advantageous or some disadvantages. So that's correct and will lead to um rapid adaptive mutations in a large population. So choice A is correct, but I'm not going to choose that as my answer. Since I do have the option of both A and B I can however, eliminate choice D, none of these since I've got one correct answer so far. So let's look at choice B. Choice B says smaller populations experience no clonal interference, stronger genetic drift. Well, let's recall what colonial interference is. So, clonal interference is the competition arising, excuse me, among lineages arising from different beneficial mutations and a sexually reproducing population. So, in a sexually reproducing population, multiple multiple mutations arise in which several might be advantageous. Um And this slows down the rate of adaptive mutation because first, the various beneficial mutations will have to out compete the wild type and then they'll compete amongst themselves to sort of prevail. Um and, and take root in the population. But in a small population, there's going to be very few to none of these beneficial mutations arising since you have that small pool, as we know, larger populations produce more mutations. So you won't have the case where you'd expect multiple beneficial mutations that need to compete against each other. So this is correct and then stronger genetic drift. Well, let's recall what genetic drift is and genetic drift is when you have a change in the frequency of alleles in a population owing to chance disappearance of particular alleles. So just by chance, not due to natural selection, you have an individual carrying a particular alil that just dies off early before it can reproduce or just fails to reproduce. Um Not because it has anything in that alley. All that is not beneficial or deleterious, but just by random chance. And of course, this will have a much greater effect, be much stronger in a small population where random chance events will be more likely to wipe out a particularly out of a population as opposed to a larger population where you'd have a larger pool of different roles. So this is correct also. So since a larger populations produce more mutant and experience more natural selection and be smaller, smaller populations experience no clonal interference and stronger genetic drift are both correct. Our correct answer for this problem will be choice. See both A and B, our reasons why ran rapid adaptive mutations will occur based on population size. See you in the next video.

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Key Concepts

Mutation as a Source of Genetic Variation

Genetic Drift and Population Size

Natural Selection vs. Random Effects in Evolution