Distribution of linkage disequilibrium with selection and finite population size

Abstract

SUMMARYThe effects of finite population size, occurring either as a bottleneck in a single generation followed by a large expansion or in all generations, are considered for models of two linked heterotic loci. Linkage is assumed to be tight because it is required if there is to be stable linkage disequilibrium,Dǂ 0, in infinitely large populations. (Dis the difference between gamete frequencies and the product of the gene frequencies.)If a substantial perturbation of frequencies occurs as a result of a bottleneck but the population is subsequently very large,Dmay take hundreds of generations to return to its stable point. In finite populations, the distribution ofDcan be ⋃-shaped, unimodal or bimodal. The correlation ofDin successive generations is higher with tight linkage and is little affected by selection or the size of the population.The utility of infinite population studies of linkage disequilibrium and its stable points is questioned, and considerable pessimism is expressed about the possibilities of distinguishing selection and sampling effects at linked loci.