Population structure with two loci

You can probably guess where this is going. With one locus I showed you that there's a deficiency of heterozygotes in a combined sample even if there's random mating within all populations of which the sample is composed. The two-locus analog is that you can have gametic disequilibrium in your combined sample even if the gametic disequilibrium is zero in all of your constituent populations. Table 1 provides a simple numerical example involving just two populations in which the combined sample has equal proportions from each population.

Table 1: Gametic disequilibrium in a combined population sample.

	Gamete frequencies				Allele frequencies
Population	$A_1B_1$	$A_1B_2$	$A_2B_1$	$A_2B_2$	$p_{i1}$	$p_{i2}$	$D$
1	0.24	0.36	0.16	0.24	0.60	0.40	0.00
2	0.14	0.56	0.06	0.24	0.70	0.20	0.00
Combined	0.19	0.46	0.11	0.24	0.65	0.30	-0.005