Genetic drift in an infinite population: The pseudohitchhiking model

Selected substitutions at one locus can induce stochastic dynamics that res emble genetic drift at a closely linked neutral locus. The pseudohitchhikin g model is a one-locus model that approximates these effects and can be use d to describe the major consequences of linked selection. As the changes in neutral allele frequencies when hitchhiking are rapid, diffusion theory is not appropriate for studying neutral dynamics. A stationary distribution a nd some results on substitution processes are presented that use the theory of continuos-time Markuv processes with discontinuous sample paths. The co alescent of the pseudohitchhiking model is shown to have a random number of branches at each node, which leads to a frequency spectrum that is differe nt from that of the equilibrium neutral model. If genetic draft, the name g iven to these induced stochastic effects, is a more important stochastic fo rce than genetic drift, then a number of paradoxes that have plagued popula tion genetics disappear.