The Hardy-Weinberg principle only predicts constant allele frequencies if certain conditions are met. These are the assumptions of the model:• Large population: so that chance events (genetic drift) do not change allele frequencies.
• Random mating: every individual is equally likely to mate with any other, whatever its genotype.
• No mutation: no new alleles are created and existing alleles are not changed.
• No migration: no individuals, and so no alleles, move into or out of the population (no gene flow).
• No natural selection: all genotypes are equally likely to survive and reproduce.The Hardy-Weinberg equations also assume the organism is diploid, reproduces sexually and has non-overlapping generations.Each condition corresponds to a process that can change allele frequencies. If any condition is broken, allele frequencies may change and the population is no longer in equilibrium. In other words, evolution is occurring.In real populations these conditions are never met perfectly. Mutation always happens at a low rate, and natural selection acts on most genes. However, many populations come close enough for the equations to give useful estimates, for example of how many people carry the allele for cystic fibrosis.Worked example: a scientist finds that the frequency of an allele in a population of beetles rose from 0.30 to 0.45 over ten generations. This shows the population is not in Hardy-Weinberg equilibrium, so at least one condition is not being met, such as selection favouring that allele.
• Random mating: every individual is equally likely to mate with any other, whatever its genotype.
• No mutation: no new alleles are created and existing alleles are not changed.
• No migration: no individuals, and so no alleles, move into or out of the population (no gene flow).
• No natural selection: all genotypes are equally likely to survive and reproduce.The Hardy-Weinberg equations also assume the organism is diploid, reproduces sexually and has non-overlapping generations.Each condition corresponds to a process that can change allele frequencies. If any condition is broken, allele frequencies may change and the population is no longer in equilibrium. In other words, evolution is occurring.In real populations these conditions are never met perfectly. Mutation always happens at a low rate, and natural selection acts on most genes. However, many populations come close enough for the equations to give useful estimates, for example of how many people carry the allele for cystic fibrosis.Worked example: a scientist finds that the frequency of an allele in a population of beetles rose from 0.30 to 0.45 over ten generations. This shows the population is not in Hardy-Weinberg equilibrium, so at least one condition is not being met, such as selection favouring that allele.