Question

How is Hardy-Weinberg's expression “(p² + 2pq + q²) = 1” derived?

Answer 1

Sum total of all the allelic frequencies is 1. Let there be two alleles A and a in a population. The frequencies of alleles A and a are ‘p’ and ‘q’ respectively.

The frequency of AA individuals in a population is p² and it can be explained that the probability that an allele A with a frequency of p would appear on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e., p².

Similarly, the frequency of aa is q² and that of Aa is 2pq.

(p² + 2pq + q²) = 1 where p² represents the frequency of the homozygous dominant genotype, 2pq represents the frequency of the heterozygous genotype and q² represents the frequency of the homozygous recessive.