Hardy-Weinberg principle says that allele frequencies in a population are stable and is constant from generation to generation.
The gene pool remains constant. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1. Individual frequencies for example can be named p.q. etc. In a diploid p and q represents the frequency of allele A and allele a.
The frequency of AA individual in a population is → p2 , in another ways i.e. the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of probabilities i.e. p2. Similarly of aa is q2, of Aa 2pq.
Hence p2 + 2pq + q = 1.
This is a binomial expansion of (p + q)2. When frequency measured, differs from expected values, the difference (direction) indicates the extent evolutionary change. Disturbance in genetic equilibrium or Hardly-Weinberg equilibrium i.e. change of frequency of allele in a population would be interpreted as resulting in evolution.
