Linkage Disequilibrium

Linkage disequilibrium can be defined as the nonrandom association of alleles present at two or more loci. It is useful in population genetics because it provides information on past events in terms of evolution, or even breeding that is occurring within or between populations. Linkage disequilibrium is calculated by estimating the allele frequencies found within a particular sample and is generally referred to as the coefficient D.  Linkage disequilibrium may be influenced by factors including genetic drift, selection, gene flow, and mutations.

The difference between the observed allele frequencies and the expected allele frequencies within a population is how the amount of linkage disequilibrium is quantified. If D is equal to 0 then a population is said to be in linkage equilibrium, meaning the allele frequencies are in expected proportions.

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