Hardy-Weinberg equilibrium: a standalone construct

Independently in 1908, the mathematician G. H. Hardy (writing in the journal Science) and the physician Wilhelm Weinberg showed that, in a large, randomly mating population, the frequencies of alleles (the alternative versions of a gene) and of genotypes (the pair of alleles an individual carries) do not change from one generation to the next when no evolutionary force is acting on them. The principle states that if the two alleles at a locus occur at frequencies p and q, then after a single generation of random mating the three genotype frequencies settle into the proportions p squared, 2pq, and q squared, and thereafter hold constant. These frequencies stay fixed only in the absence of natural selection, genetic drift, migration, mutation, and non-random mating, so the result works as a null model: a population whose observed counts depart from the expected proportions signals that one of those forces, that is, evolution, is at work. Hardy-Weinberg equilibrium is a landmark because it gives population genetics a fixed baseline against which real allele and genotype data can be tested, and it underlies routine work from carrier-frequency estimates in medical genetics to quality checks on modern genotyping datasets.[1][2][3]

Unit

A frequency equilibrium at a genetic locus, expressed for two alleles as the genotype proportions p squared, 2pq, and q squared

Recovery means

Not applicable

Measured by

Assessed by comparing observed genotype counts against the expected p squared, 2pq, q squared proportions, usually with a chi-square or exact goodness-of-fit test