We ran a simulation that graphed the popuulation and allele frquencies (A and B

Question

We ran a simulation that graphed the popuulation and allele frquencies (A and B alleles) of three populations. For a simulation where there is no genetic drift, mutation or migration affecting the population, there is still a slow, steady change of the frequency of the A allele over time (all three poplations' allele A frquencies seemed to go towards an allele frequency of 0.500).

a) What is the factor causing the linear curves to all go slowly and steadily towards an allele frequency of 0.500?

b) How is it that allele frequencies can still fluctuate in absence of genetic drift, migration and mutation?

Explanation / Answer

There are 5 main factors that can affect allele frequency in a population, which are evolution, natural selection, mutations, migration and genetic drift.

Evolution is a slow process triggered by changes in the environment, due to the fact that some alleles in a gene pool do better than others. Evolution is the result of changes in allele frequency along generations, therefore is a term used for populations and not individuals. Evolution can be caused by natural selection, mutation, migration, and genetic drift. Natural selection, on the other hand, is caused when a population produces more offspring than environmental resources in their habitat. The best-adapted individuals will be the ones getting the resources and surviving causing their survival and therefore a change in the frequency of the alleles in the initial population. In this case, the frequency of the allele A is the one that slowly starts to decrease towards a 0.5 frequency.

Mutations cause a fast change in the allele frequency, as they are the source of new alleles, and they are essential for evolution to take place. In the case of migration, the flow of genes between populations (native and migrant) causes changes in their allele frequencies.

a) What is the factor causing the linear curves to all go slowly and steadily towards an allele frequency of 0.500?

Natural selection and genetic linkage: Natural selection is caused by an overgrowth of the population that will push individuals to start competing for limited resources (not enough now due to overpopulation), and only the best-adapted individuals will be the ones getting them, which will increase the frequency of their alleles in the population. So for example, for the three populations, there were other alleles that made some of the individuals less adapted to the environment, which inheritance was linked with the A allele (both alleles closely located in a chromosome), therefore the frequency of the allele A started decreasing. In summary natural selection and genetic linkage.

b) How is it that allele frequencies can still fluctuate in absence of genetic drift, migration and mutation?

By natural selection, as is the other factor that causes evolution in a gene pool

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