Question

If the allele frequency of A is 0.20, what would be the expected number of heterozygotes in a population of 200 individuals, assuming HWE and that there are two alleles in the population?

Answer 1

If there are two alleles for the locus in question, lets say the other allele is "a". Further, say frequency of A or freq(A)=p and freq(a)=q. Now, if p= 0.20, then q= 1-0.20=0.80.

According to Hardy -Weinberg principle, p2+2pq+q2=1, where p2 is the genotype frequency of AA homozygotes, q2 is the genotype frequency of aa homozygotes, and 2pq is the genotype frequency of the heterozygotes.

Given, p=0.20, deduced, q=0.80, then genotype frequency for heterozygotes is expected to be 2pq=2*0.20*0.80=0.32.

This means the probability of someone to be a heterozygote for the locus in question in the population is 0.32. In other words, 32% of the population are heterozygotes. hence, expected number of heterozygotes in a population of 200 would be= 200*0.32=64.