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

(b) List any two factors that can disturb the genetic equilibrium.



  1. Sum Total of All the Allele 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 p 2 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., p 2 . Similarly, the frequency of aa is q 2 and that of Aa is 2pq.p 2 + 2pq+q 2 ) = 1,where p 2 represents the frequency of homozygous dominant genotype, 2pq represents the frequency of the heterozygous genotype and q 2 represents the frequency of the homozygous recessive.
  2. Factors that affect Hardy–Weinberg equilibrium:
  1. Gene migration or gene flow
  2. Genetic drift
  3. Mutation
  4. Genetic recombination
  5. Natural Selection


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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.