AP Bio Study Guide

Big Idea 1.A

What are the conditions for Hardy-Weinberg equilibrium?

Hardy-Weinberg equilibrium is the state where a population is stable and non-evolving. This means that allelic frequencies are not changing (i.e. if the frequency of a particular allele is 25% now, it will be 25% in 1,000 years).

For a population to be in Hardy-Weinberg equilibrium, the following conditions must be true:

  • The population must be very large. No small changes can have major effects.
  • The population must be isolated from other populations. No new genes can be introduced.
  • There are no mutations. Mutations could change frequencies or introduce a new allele.
  • Mating must be random. Otherwise, better adapted mates will have a reproductive advantage.
  • No natural selection. Natural selection causes changes in relative frequencies of alleles.

Since 2015, students no longer need to be able to apply the Hardy-Weinberg equilibrium equation.