Question

A particular gene has two alleles, a dominant allele A and a recessive allele a. The frequency of allele A is 0.55. If the population is in Hardy-Weinberg equilibrium with respect to the gene, then what is the expected frequency of genotype Aa

Answer 1

If p = frequency of A and q = frequency of a, then assuming H-W equilibrium we have

p + q = 1   ⇒   q = 1 - p = 1 - 0.55 = 0.45

Then the expected frequency of the heterozygous genotype Aa is 2pq = 2 • 0.55 • 0.45 = 0.495.