Practice question

Allele frequency can be derived accurately from genotype frequencies using gene counting method. Each AA individual contributes two A alleles, heterozygote contributes one of each type. Therefore p equals frequency of AA plus half frequency of Aa. With AA equals 0.25 and Aa equals 0.5, p equals 0.25 plus 0.25 equals 0.5, and q also 0.5. When genotype frequencies already follow Hardy-Weinberg expectation, this estimate coincides with square root of AA. Such estimation is fundamental for population screening and for testing whether observed counts deviate from equilibrium proportions within studied cohort.