hardy-weinberg equation

• hardy-weinberg principle: if certain conditions are met, the allele frequencies of a gene within a population will not change from one generation to the next
• conditions or assumptions that must be met for the hardy-weinberg principle to hold true:

  • mating must be random between individuals
  • population is infinitely large (no genetic drift)
  • there is no gene flow, mutation or natural selection
• the hardy-weinberg equation allows for the calculation of allele and genotype frequencies within populations

  it also allows for predictions to be made about how these frequencies will change in future generations
• if the allele frequencies in a population change overtime, then it means that migration, mutation or natural selection has happened
• if the phenotype of a trait in a population is determined by a single gene with only 2 alleles then the population will consist of individuals with three possible genotypes

  homozygous dominant (BB)

  heterozygous (Bb)

  homozygous recessive (bb)
• when using the hardy-weinberg equation, the frequency of a genotype is represented as a proportion of the population

  e.g the BB genotype could be 0.40

  whole population = 1

  the letter p represents the frequency of the dominant allele (B)

  the letter q represents the frequency of the recessive allele (b)

  as there are only 2 alleles at a single gene locus for this phenotypic trait in the population: p + q = 1
• the chance of an individual being homozygous dominant and is p^2

  in this instance, the offspring would inherit dominant alleles from both parents (p x p = p^2)
• the chance of an individual being heterozygous is 2pq

  • offspring could inherit a dominant allele from the father and a recessive allele from the mother or vice versa (p x q) = 2pq
• the chance of an individual being homozygous recessive is q^2

  in this instance, the offspring would inherit recessive alleles from both parents (q x q = q^2)
• as these are all possible genotypes of individuals in the population, the following equation can be constructed:

  p^2 + q^2 + 2pq = 1
• gene flow - movement of genes / alleles into or out of a population