Population Genetics Question:
Consider a locus with two alleles, A and a. The frequencies of the two homozygotes are both 0.4. What genotype is selected against? What is the selection coefficient s?
Answer :)
Two homozygotes for allele A and a are AA and aa.
Genotype frequencies of AA = 0.4
Genotype frequencies of aa = 0.4
The homozygous dominant genotype should have higher genotype frequency than a homozygous recessive genotype. Therefore, AA is selected against.
Because AA is selected against, the genotype frequency of AA should have here 0.6 in HW equilibrium.
Therefore, survival rate = 0.4/0.6
Therefore, survival rate = 0.67
The survival rate of aa genotype is 100% because it is not selected against.
Fitness of aa = 100/100
Fitness of aa = 1
Fitness of AA = 0.67/1
Fitness of AA = 0.67
The selection coefficient s = 1 – 0.67
The selection coefficient s = 0.33
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