Subpopulations

Heterozygote deficiency in sub-populations with differing allele frequencies:
Wahlund Effect

    Two sub-populations of a single species differ in allele frequency at a locus. In Sub-population 1, q = 0.75 and in Sub-population 2, q = 0.25; in both populations the observed frequency of heterozygotes is 6 / 16 = 0.375, which is equal to the expected frequency (2)(0.75)(1 - 0.75)(16) = 0.375.

    If the two sub-populations were treated as a single population,
the observed allele frequencies would be q = 0.50: the expected frequency of heterozygotes = (2)(0.50)(1 - 0.50) = 0.500. The deficiency of heterozygotes is (Hexp - Hobs) / Hexp = (0.500 - 0.375) / 0.500 = 0.25.

    This deficiency of heterozygotes from expectation is called the Wahlund Effect, after the scientist who first observed it in combining genetic data from two cod populations from different parts of the Baltic Sea and the waterways leading into it.



Text material © 2020 by Steven M. Carr