LD can also be created in populations that have recently experienced a reduction in population size (bottleneck) with accompanying extreme genetic drift (7). During a bottleneck, only few allelic combinations are passed on to future generations. This can generate substantial LD. In human genetic studies, populations that have undergone severe bottlenecks (e.g., Finnish and Afrikaner populations) have been used in LD mapping a number of disease traits (19). Selection, which produces locus-specific bottlenecks, also causes LD between the selected allele at a locus and linked loci. Moreover, selection for or against a phenotype controlled by two unlinked loci (epistasis) may result in LD despite the fact that the loci are not physically linked.