1 Answers
Additive disequilibrium is a statistic that estimates the difference between observed genotypic frequencies and the genotypic frequencies that would be expected under Hardy–Weinberg equilibrium. At a biallelic locus with alleles 1 and 2, the additive disequilibrium exists according to the equations
where fij is the frequency of genotype ij in the population, p is the allele frequency in the population, and D is the additive disequilibrium coefficient.
Having a value of D > 0 indicates an excess of homozygotes/deficiency of heterozygotes in the population, whereas D < 0 indicates an excess of heterozygotes/deficiency of homozygotes. When D = 0, the genotypes are considered to be in Hardy Weinberg Equilibrium. In practice, the estimated additive disequilibrium from a sample, D ^ {\displaystyle {\widehat {D}}} , will rarely be exactly 0, but it may be small enough to conclude that it is not significantly different from 0. Finding the value of the additive disequilibrium coefficient provides an alternative assessment in accepting or rejecting Hardy Weinberg Equilibrium in a set of genotypic frequencies.
Because the genotype and allele frequencies must be positive numbers in the interval , there exists a constraint on the range of possible values for D, which is as follows: