05 Origin and Evolution of life - part 09 - Hardy-Weinberg's principle

05 Origin and Evolution of life - part 09 - Hardy-Weinberg's principle


Hardy-Weinberg's principle :
  • It is also known as Hardy-Weinberg's equilibrium law. 
  • The law states that `at equilibrium point both the gene (allele) frequency and geneotypic frequency remain constant from generation to generation'. 
  • It occurs only in the diploid, sexually reproducing, large, free interbreeding population in which mating is random and no selection or other factors are present for changing the allele frequency. 
  • e.g. A single locus has two alleles (A and a). The frequencies of these allele are p and qrespectively. 
  • The allele frequency for any locus is always one. i.e. P + Q = 1. 
  • The genotypic frequencies of both the alleles are represented by (p + q)2 = 1. 
  • The binomial expansion of this is P2 + 2pq + q2= 1 
  • i.e. AA=P2, aa=q2 and for 2Aa= 2pq. Hence P2 + 2pq + q2 = 1 
  • This is a binomial expansion of (p + q)2. This can be explained by punnet square as follow.
  • Like allele frequency, the genotypic frequencies together are also equal to 1.
  • There are few factors such as gene migration (gene flow), genetic drift, mutation, genetic recombinations, natural selection, nonrandom mating, etc. which affect or change the Hardy-Weinberg equilibrilium. 
  • If these factors do not occur in the population, then population is genetically stable or non evolving population.

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