DYNAMICS OF REPEAT POLYMORPHISMS UNDER A FORWARD-BACKWARD MUTATION MODEL - WITHIN-POPULATION AND BETWEEN-POPULATION VARIABILITY AT MICROSATELLITE LOCI

Suggested molecular mechanisms for the generation of new tandem repeat s of simple sequences indicate that the microsatellite loci evolve via some form of forward-backward mutation. We provide a mathematical bas is for suggesting a measure of genetic distance between populations ba sed on microsatellite variation. Our results indicate that such a gene tic distance measure can remain proportional to the divergence time of populations even when the forward-backward mutations produce variable and/or directionally biased alleles size changes. If the population s ize and the rate of mutation remain constant, then the measure will be proportional to the time of divergence of populations. This genetic d istance is expressed in terms of a ratio of components of variance of allele sizes, based on expressions developed for studying population d ynamics of quantitative traits. Application of this measure to data on 18 microsatellite loci in nine human populations leads to evolutionar y trees consistent with the known ethnohistory of the populations.