Mixing of diverged populations

The mixing of two genetically diverged populations, often termed admixture, can produce substantial levels of gametic disequilibrium. This is caused by different allele frequencies in the two source populations that result in different gamete frequencies at gametic equilibrium. Recombination acts to produce independent segregation but it does so only based on the allele frequencies within a group of mating individuals. Table 2.13 gives an example of gametic disequilibrium produced when two populations with diverged allele frequencies are mixed equally to form a third population. In the example, the allele-frequency divergence is large and admixture produces a new population where gametic disequilibrium is 64% of its maximum value. In general, gametic disequilibrium due to the admixture of two diverged populations increases as allele frequencies become more diverged between the source populations, and the initial composition of the mixture population approaches equal proportions of the source populations.

Table 2.13 Example of the effect of population admixture on gametic disequilibrium. In this case the two populations are each at gametic equilibrium given their respective allele frequencies. When an equal number of gametes from each of these two genetically diverged populations are combined to form a new population, gametic disequilibrium results from the diverged gamete frequencies in the founding populations. The allele frequencies are: population 1 p1 = 0.1, p2 = 0.9, q1 = 0.1, q2 = 0.9; population 2 p1 = 0.9, p2 = 0.1, q1 = 0.9, q2 = 0.1. In population 1 and population 2 gamete frequencies are the product of their respective allele frequencies as expected under independent segregation. In the mixture population, all allele frequencies become the average of the two source populations (0.5) with Dmax = 0.25.

Gamete/D Gamete frequency Population 1 Population 2 Mixture population

Recombination rate (r) = G.SG

Recombination rate (r) = G.GS

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