Question

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 #1

**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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