Hardy-Weinberg Equilibrium

Hardy-Weinberg equilibrium is a fundamental principle in population genetics that describes the genetic composition of a population when certain conditions are met. It provides a mathematical framework to understand how genetic traits are inherited and how they may change over time within a population.

The principle is based on several assumptions:

1. Large population size: The population is assumed to be infinitely large or, more practically, large enough to ignore random fluctuations due to sampling.

2. Random mating: Individuals in the population mate randomly with respect to the trait under consideration. This means that there is no preference or selection for certain genotypes when choosing a mate.

3. No migration: There is no migration into or out of the population, which means no new genetic material is introduced or lost.

4. No mutation: There are no new genetic mutations occurring in the population. This assumption is often violated in reality, but it is useful to understand the equilibrium state.

5. No selection: There is no differential survival or reproductive advantage for individuals with different genotypes. In other words, all genotypes have equal fitness.

Under these assumptions, the Hardy-Weinberg equilibrium describes the relationship between allele and genotype frequencies in a population from one generation to the next. According to the equilibrium, the frequencies of alleles and genotypes remain constant over time, and the population reaches a stable genetic equilibrium.

The equilibrium can be mathematically described using the Hardy-Weinberg equations:

1. Allele frequency equation: p + q = 1
   

   • p represents the frequency of one allele (usually the dominant allele)

   • q represents the frequency of the other allele (usually the recessive allele)

   • Together, p and q add up to 1, representing all possible alleles in the population.

1. Genotype frequency equation: p^2 + 2pq + q^2 = 1
   

   • p^2 represents the frequency of the homozygous dominant genotype (AA)

   • 2pq represents the frequency of the heterozygous genotype (Aa)

   • q^2 represents the frequency of the homozygous recessive genotype (aa)

   • Together, the sum of these genotype frequencies is equal to 1, representing the entire population.

These equations allow us to determine the expected allele and genotype frequencies in a population if the Hardy-Weinberg equilibrium is maintained. Deviations from the expected frequencies indicate that evolutionary forces, such as mutation, migration, selection, or non-random mating, are acting on the population.

Overall, the Hardy-Weinberg equilibrium provides a useful baseline for understanding the distribution of genetic traits in populations and serves as a reference point for studying evolutionary processes.