Disequilibrium, selection, and recombination: limits in two-locus, two-allele models.

All possible combinations of equilibria and fitnesses in two-locus, two-allele, deterministic, discrete-generation selection models are enumerated. This knowledge is used to obtain limits (which can be calculated to arbitrary precision) to the relationships among disequilibrium, selection and recombination for fixed values of allele frequencies. In all cases, the inequality magnitude of rD less than s/10 holds, where r is recombination and D is disequilibrium, and all selection coefficients lie between 1 - s and 1 + s times that of the double heterozygote. Linear programming techniques are used to observed nonzero values of D reported in the literature. One conclusion is that the failure to observe nonzero values of D is not surprising.