Hardy-Weinberg equilibrium states that there is a balance in the frequency of alleles from generation to generation within a large population over a period of time assuming that : (i) mating is random; (ii) there is no natural selection; (iii) there is no migration; (iv) there is no mutation. He also stated that sum of all allelic frequency is 1. In such a stable population, for a gene with two alleles, A (dominant) and a (recessive), the frequency of both allele is denoted as p and q respectively. Then the frequencies of the three possible genotypes (AA, Aa, and aa) can be expressed by the equation : p2 + 2pq + q2 = 1.

where p2 = frequency of AA (homozygous dominant) individuals, 2pq = frequency of Aa (heterozygous) individuals, and q2 = frequency of aa (homozygous recessive) individuals