HARDY-WEINBERG PRINCIPLE
• The genetic equilibrium is defined as "The relative frequencies of various kinds of genes in a large and randomly mating sexual panmictic population tend to remain constant from generation to generation in the absence of mutation, selection and gene flow." This is called Hardy-Weinberg principle or Hardy-Weinberg equilibrium.
• Hardy-Weinberg principle is an expression of the notion of a population in 'genetic equilibrium' and is the basic principle of population genetics.
• In a population at equilibrium, for a locus with two alleles, D and d having frequencies of p and q, respectively, the genotype frequencies are: DD=p², Dd = 2pq, and dd =q².
The two formulae are
p² + 2pq- q² = 1.
where, ( p + q = 1 )
p-Frequency of the dominant allele in the population. q- Frequency of the recessive allele in the population.
p²2= Percentage of homozygous dominant individuals. q² = Percentage of homozygous recessive individuals. 2pq = Percentage of heterozygous individuals.
1 = Sum total of all the allelic frequencies. Hardy-Weinberg's law describes a theoretical situation in which a population is undergoing no evolutionary change.
• Salient features of Hardy-Weinberg principle: (i) random mating, (ii) large population size, (iii) biparental mode of reproduction and (iv) homogeneous age structure. The gene frequency will remain static only in the absence of evolutionary forces like mutations, selection, genetic drift and migration.
Significance of Hardy-Weinberg principle
• The Hardy-Weinberg law is important primarily because it describes the situation in which there is genetic equilibrium and no evolution. Thus
It provides a theoretical baseline for measuring evolutionary change.
• The equilibrium tends to conserve gains which have been made in the past and also to avoid too rapid changes.
• Equilibrium maintains heterozygosity in the population. Equilibrium prevents evolutionary progress.`
Factors affecting Hardy-Weinberg's principle are:
(i) gene flow/ gene migration,
(ii) genetic drift,
(iii) genetic recombination,
(iv) mutations and
(v) natural selection.