HINT 23O: Write the frequencies of the four genotypes at the start of the generation as {1/4 + D, 1/4 – D, 1/4 – D, 1/4 + D}, where D is the strength of linkage disequilibrium (p. 433); then, find how these change as a result of selection within patches. Recall that random mating halves the linkage disequilibrium between unlinked loci (p. 434).