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Hardy Weinberg Equilibrium – Importance, Statement and Infringement

Grade 10
May 3, 2023

Hardy Weinberg Equilibrium

In the absence of disruptive factors, genetic variation in a population will remain constant from generation to generation, according to the Hardy-Weinberg equilibrium. The rule says that when mating is random in a large population with no disruptive events, both genotype and allele frequencies will remain constant since they are in equilibrium.

Various causes can disrupt the Hardy-Weinberg equilibrium, including mutations, natural selection, non-random mating, genetic drift, and gene flow. Mutations, for example, disrupt the equilibrium of allele frequencies by introducing new alleles into a population.

Natural selection and non-random mating destabilize the Hardy-Weinberg equilibrium by causing variations in gene frequencies. This happens because specific alleles either promote or hinder the reproductive success of the organisms that bear them.

Genetic drift, which happens when allele frequencies become higher or lower by chance and often occurs in small populations, is another factor that might disrupt this balance. Finally, gene flow, which happens when two populations reproduce and introduce new alleles into a population, may also change the Hardy-Weinberg equilibrium.


Because all these disruptive factors are widespread in nature, the Hardy-Weinberg equilibrium seldom holds true in practice. As a result, the Hardy-Weinberg equilibrium defines an optimal state, and genetic variability in nature may be quantified as deviations from this perfect state.

Hardy Weinberg equilibrium

Hardy Weinberg Law Statement

  • “In the absence of any evolutionary influences from generation to generation, genotype and allele frequencies in a large, random-mating population remain constant.” Natural selection, genetic drift, and mutation are all examples of evolutionary processes.
  • Genotype frequencies and allele frequencies are connected in such a way that the square expansion of such allele frequencies is obtained. In other words, the rule states that, given the frequency of distinct alleles in a population, predicting the anticipated frequencies of genotypes under a particular limited set of assumptions is feasible.

Hardy Weinberg law

Consider a single locus with only two alleles denoted by A and a, with corresponding frequencies f(A) = p and f(a) = q, respectively. Then, the genotype frequencies that can be expected under the limited condition of random mating are:

  • For AA homozygotes, f(AA) = p2.
  • For aa homozygotes, f(aa) = q2.
  • For heterozygotes, f(Aa) = 2pq.

The Hardy-Weinberg Equation can be represented by:

p2 + q2 + 2pq = 1

Assumptions of Hardy Weinberg law 

A couple of the law’s assumptions are as follows:

  • Sexual reproduction is the only type of reproduction that may take place.
  • Mating occurs at random.
  • The population is infinitely big.
  • Entities are diploid.
  • There is no generational overlap.
  • There is equality of allele frequencies across sexes.
  • There is no evidence of gene flow, selection, mutation, migration, or mixing.

Any deviation from the intended outcome can occur if the assumptions mentioned above are violated. The implications are entirely dependent on the deviated deduction.

Genotype frequencies

The law states that after a single generation of random mating, a population must exhibit Hardy Weinberg proportions (given genotypic frequencies). Therefore, if the assumption of random mating is violated, this population will lack Hardy Weinberg proportions. The most common cause of non-random mating is inbreeding. It causes an increase in the homozygosity of all genes.

Infringement of Hardy Weinberg Equilibrium

Breaching any of these four assumptions will result in the population retaining the Hardy–Weinberg proportions at each generation, but the allele frequencies will shift over time.

  • Mutation: Mutation has a minor effect on allele frequencies. The mutation rate ranges from 10-4 to 10-8. The majority of allele frequency changes are of this kind. Even if there is a strong selection against the alleles in the population, recurrent mutations will keep it.
  • Selection: This usually results in a fast shift in allele frequencies. Few selection forms, especially balancing selection, can end in equilibrium with no loss of alleles, but others, such as directional selection, can eventually result in allele loss.

Genetic diversity

  • Size of the population: A tiny population might result in a random change in allele frequencies, which can be linked to the sampling phenomenon known as genetic drift. Sampling effects are substantial when alleles are found in fewer copies.
  • Migration: Two or more groups can be genetically connected with migration. In this case, the allele frequencies in the populations tend to grow increasingly homozygous. The Wahlund effect is essentially a few migration models (non-random mating). For such models, Hardy–Weinberg proportions are frequently incorrect.

Importance of Hardy Weinberg Equilibrium

  • The Hardy-Weinberg equilibrium is useful in analyzing genetic variation in a population and comparing it to the estimated value from the Hardy-Weinberg law if the population is in equilibrium.
  • When the actual frequency in a population differs from the predicted value, it indicates a disturbance and a violation of one or more assumptions.
  • It also aids in calculating the number of heterozygous bearers of a dangerous recessive gene.

Hardy Weinberg law

Hardy Weinberg Equilibrium


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