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Essay 2 - 1 We know that natural selection can result in...

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1) We know that natural selection can result in changes in allele frequencies. Is it possible to have natural selection operating in a population with no resultant evolutionarily change? If not, explain why? If so, describe a situation where this can occur. - It is possible to have natural selection operating in a population w/ no resultant evolutionarily change. If there is very little genetic variance in a population, selection even at its highest would be useless b/c there is not much different allele to act on and to create change in allele frequency (evolution). An example is when we add selection to the hardy Weinberg equilibrium. For instance, the allele frequency for a certain population is equal starting out and after viability selection that could change the genotype frequencies. However, if the allele frequency remains the same after selection, then we would not resulted in evolution. 2) Biologists were surprised when it was discovered that the rate of neutral substitution is not dependent on population size. Explain: 1) why you might expect that the neutral substitution rate would depend on population size, and 2) why it does not. (Please explain part 2 in words; Do Not just gives the relevant equation(s). - It must be, however, emphasized that the percentage of mutations that fall in the category of selectively neutral does depend on the size of the population. When the selective coefficient is less than 1/Ne in a given population. This means that a greater percentage of mutations fall in the category of effectively neutral mutation in a small population than in large population. As MOST mutations have a negative selection coefficient and only a minority have a positive selection coefficient and b/c the probability of fixation of negative mutation is substantially smaller than the prob. of fixation of positive or selectively neutral mutation, the total # of mutations fixed by drift over time i.e. the substitution rate is greater in a small population size than in a large
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