A population originally has 500 males and 500 females, all of whom breed. A hurr

Question

A population originally has 500 males and 500 females, all of whom breed. A hurricane greatly reduces the population’s size to 10 males and 10 females. The original population had an approximately equal number of blue eye color alleles and brown eye color alleles. The population after the hurricane has a blue eye color allele frequency of 0.9 and a brown eye color allele frequency of 0.10. What type of event has this population experienced causing it to become so small and what is the probability that the brown eye color allele will become fixed in this population? If the brown eye does become fixed in this population, which force of evolution is most likely responsible for its fixation?

Explanation / Answer

This is the case of Genetic drift and to more specifically of Bottleneck effect where a sudden catastrophic event has reduced the population size drastically. Since the allele frequency of blue color is 0.9, there is 0.9 probability (90 percent chances) of that being fixed (meaning it will be the only allele in the population after infinite matings) and fixation probability for the brown allele is 0.1. If it does get fixed, then natural selection might be the possible force. If the allele for brown eyes has an advantage over the allele for blues eyes the frequency will be driven in that direction.

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