Hardy-Weinberg problems look at the dominant and recessive traits of a population and determine the percentage of homozygous dominant, homozygous recessive and heterozygous individuals in the population. The Hardy-Weinberg equation is a mathematical expression that is utilized to calculate the genetic variation in a large population. The equation can only be used when a population is in Hardy-Weinberg equilibrium.
The Hardy-Weinberg equation is p^2 + 2pq + q^2 = 1. In the equation, p + q also must equal 1. For two alleles of a genetic locus, p^2 is the frequency of the homozygous dominant allele, q^2 is the frequency of the homozygous recessive allele and 2pq is the frequency of the heterozygotes in the population.
Problems that utilize the Hardy-Weinberg equation ask about the frequency of the different alleles in a population. Frequency numbers can then be converted to percentages. A typical Hardy-Weinberg problem will give the student the number of individuals in the population and the frequencies of either the dominant allele or the recessive allele. With that information, students can mathematically determine the remaining variables to ultimately determine the relative frequencies of the population. In research settings, this equation is utilized to determine if the observed genotype frequencies differ from the predicted frequencies from the equation.