Hardy Weinberg Principle – Class 12 | Chapter – 7 | Biology Short Notes Series PDF

Hardy Weinberg Principle: The law is named after G.H. Hardy and Wilhelm Weinberg. They were pioneers in mathematically illustrating this principle, also referred to as Hardy–Weinberg equilibrium, theorem, law or model. Hardy’s thesis centrally paid attention to debunking the view that prevailed in those times that a dominant allele has the tendency to increase in frequency automatically. In today’s times, the uncertainty on selection and dominance is not very remarkable. In the current times, the Hardy-Weinberg genotype frequency tests are applied to evaluate population stratification and other sorts of non-random mating.

Hardy Weinberg principle

  • This principle states that allele frequencies in a population are stable and is constant from generation to generation, the gene pool remains constant. This is referred to as genetic equilibrium where the sum total of all allelic frequencies is 1.
  • In a diploid, let p and q represent frequency of allele A and a. The probability that an allele A with a frequency of p appears on both the chromosomes of a diploid individual is simply the product of the probabilities.
  • Five factors affecting Hardy-Weinberg principle are – gene flow, genetic drift, genetic recombination, mutation and natural selection
  • When the original drifted population becomes founders, the effect is known as founder effect

Assumptions of Hardy Weinberg principle

  • In order to maintain equilibrium, only sexual reproduction can occur.
  • Individuals of the population should randomly mate.
  • The size of the population should be indefinitely large, and there must be diploid entities.
  • Entities are diploid.
  • The generations must not overlap, and the sex ratio should be equal.
  • Equality of allele frequencies in terms of sexes
  • No traces of gene flow, selection, mutation, migration or admixture.

Equation of Hardy Weinberg principle

The Hardy-Weinberg equation can be explained by considering a simple genetic locus containing two alleles, A and a. The equation can be written as-

p2 + 2pq + q2 = 1

where p is the frequency of the allele “A” and q is the frequency of allele “a”. p2 denotes the frequency of the homozygous genotype AA, q2 indicates the frequency of the homozygous genotype aa, and 2pq represents Aa, which is the frequency of the heterozygous genotype. In studies related to population genetics, the Hardy-Weinberg equation is used to compute the difference between the observed genotype frequencies and the calculated frequencies given by the equation.


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By Team Learning Mantras