The document discusses the Hardy-Weinberg principle of population genetics. It states that the frequency of alleles in a population will remain constant over generations if the population is large, randomly mating, and not subject to mutations, gene flow, or selection pressures. It provides an example using cat coat color alleles to demonstrate calculating genotype frequencies based on observed phenotypes and applying the Hardy-Weinberg equations. Factors that can disrupt Hardy-Weinberg equilibrium and cause allele frequencies to change are also noted, including mutation, migration, natural selection, and genetic drift.