Explain Hardy-Weinberg law of equilibrium and mention the factors that upset the equilibrium. (IAS 2022/10 Marks)

Hardy-Weinberg Law of Equilibrium

The Hardy-Weinberg law states that allele frequencies in a population will remain constant from generation to generation, provided that certain conditions are met.

• Mathematical Expression: The frequencies of alleles and genotypes in a population can be expressed using the following formula:
  
  • p² + 2pq + q² = 1
  • Where:
    
    • p = frequency of the dominant allele.
    • q = frequency of the recessive allele.
    • p² = frequency of homozygous dominant individuals.
    • q² = frequency of homozygous recessive individuals.
    • 2pq = frequency of heterozygous individuals.

Conditions for Hardy-Weinberg Equilibrium

• Large Population Size: A large population size ensures that genetic drift, which causes random fluctuations in allele frequencies, is minimized.
• No Mutation: There must be no mutations in the genetic material that could introduce new alleles into the population.
• No Migration: There should be no gene flow through migration, as it can introduce or remove alleles from the population.
• Random Mating: Mating must be random, meaning individuals are not selecting mates based on genetic characteristics.
• No Natural Selection: All individuals must have an equal chance of survival and reproduction, regardless of their genotype.

Factors That Upset Hardy-Weinberg Equilibrium

• Genetic Drift:
  
  • Random changes in allele frequencies due to the small size of a population.
  • Can lead to the loss of alleles or fixation of certain alleles by chance.
• Mutation:
  
  • New mutations introduce new alleles into the gene pool, which can change allele frequencies.
  • Mutations are a source of genetic variation and can upset the equilibrium.
• Gene Flow (Migration):
  
  • The movement of individuals into or out of a population can introduce new alleles or alter existing allele frequencies.
  • This disrupts the genetic structure of the population.
• Non-Random Mating:
  
  • If individuals choose mates based on certain genetic traits, it can affect the frequency of alleles.
  • Inbreeding (mating between closely related individuals) can lead to a higher proportion of homozygous individuals.
• Natural Selection:
  
  • Differential survival and reproduction based on genotype result in certain alleles becoming more common while others become less frequent.
  • Natural selection favors individuals with advantageous traits, leading to a shift in allele frequencies.

Conclusion

The Hardy-Weinberg law of equilibrium provides a theoretical framework to understand the genetic equilibrium in populations. However, various factors such as mutation, gene flow, genetic drift, and natural selection can disrupt this equilibrium and lead to changes in allele frequencies over time.