Microsatellite diversity and the demographic history of modern humans

Abstract

We have examined differences in diversity at 60 microsatellite loci among human population samples from three major continental groups to evaluate the hypothesis of greater African diversity in this rapidly evolving class of loci. Application of a statistical test that assumes equal mutation rates at all loci fails to demonstrate differences in microsatellite diversity, while a randomization test that does not make this assumption finds that Africans have significantly greater microsatellite diversity (P < 10(-8)) than do Asians and Europeans. Greater African diversity is most apparent at loci with smaller overall variance in allele size, suggesting that the record of population history has been erased at repeat loci with higher mutation rates. A power analysis shows that only 35-40 microsatellites are needed to establish this difference statistically, demonstrating the considerable evolutionary information contained in these systems. On average, African populations have approximately 20% greater microsatellite diversity than do Asian and European populations. A comparison of continental diversity differences in microsatellites and mtDNA sequences suggests earlier demographic expansion of the ancestors of Africans.

Figure 1

A plot of type II error (the probability of falsely accepting the null hypothesis of no increase in genetic diversity) as a function of the number of microsatellite loci. Type I error (the probability of falsely rejecting the null hypothesis) has been fixed at 0.05.

Figure 2

A plot of the first two principal coordinates of the mean allele sizes of each population, showing the genetic relationships of 15 subpopulations.