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In population genetics, the Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem, or law, states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
A de Finetti diagram. The curved line is the expected Hardy–Weinberg frequency as a function of p.. A de Finetti diagram is a ternary plot used in population genetics.It is named after the Italian statistician Bruno de Finetti (1906–1985) and is used to graph the genotype frequencies of populations, where there are two alleles and the population is diploid.
The Hardy–Weinberg law describes the relationship between allele and genotype frequencies when a population is not evolving. Let's examine the Hardy–Weinberg equation using the population of four-o'clock plants that we considered above: if the allele A frequency is denoted by the symbol p and the allele a frequency denoted by q, then p+q=1.
This point always has a lower heterozygosity (y value) than the corresponding (in allele frequency p) Hardy-Weinberg equilibrium. In population genetics, the Wahlund effect is a reduction of heterozygosity (that is when an organism has two different alleles at a locus) in a population caused by subpopulation structure.
Genetic equilibrium describes a theoretical state that is the basis for determining whether and in what ways populations may deviate from it. Hardy–Weinberg equilibrium is one theoretical framework for studying genetic equilibrium. It is commonly studied using models that take as their assumptions those of Hardy-Weinberg, meaning:
Similarly, we can also test for Hardy Weinberg Equilibrium using the z-statistic, which uses information from the estimate of additive disequilibrium to determine significance. When using the z- statistic, however, the goal is to transform the statistic in a way such that asymptotically , it has a standard normal distribution .
In the absence of population structure, Hardy-Weinberg proportions are reached within 1–2 generations of random mating. More typically, there is an excess of homozygotes, indicative of population structure. The extent of this excess can be quantified as the inbreeding coefficient, F. Individuals can be clustered into K subpopulations.
A population that satisfies these conditions is said to be in Hardy–Weinberg equilibrium. In particular, Hardy and Weinberg showed that dominant and recessive alleles do not automatically tend to become more and less frequent respectively, as had been thought previously. The conditions for Hardy-Weinberg equilibrium include that there must be ...