CHROMOSOME-Y MICROSATELLITES - POPULATION GENETIC AND EVOLUTIONARY ASPECTS

By means of a multicenter study, a large number of males have been cha racterized for Y-chromosome specific short tandem repeats (STRs) or mi crosatellites. A complete summary of the allele frequency distribution s for these Y-STRs is presented in the Appendix. This manuscript descr ibes in more detail some of the population genetic and evolutionary as pects for a restricted set of seven chromosome Y STRs in a selected nu mber of population samples. For all the chromosome Y STRs markedly dif ferent region-specific allele frequency distributions were observed, a lso when closely related populations were compared. Haplotype analyses using AMOVA showed that when four different European male groups (Ger mans, Dutch, Swiss, Italians) were compared, less than 10% of the tota l genetic variability was due to differences between these populations . Nevertheless, these pairwise comparisons revealed significant differ ences between most population pairs. Assuming a step-wise mutation mod el and a mutation frequency of 0.21%, it was estimated that chromosome Y STR-based evolutionary lines of descent can be reliably inferred ov er a time-span of only 1950 generations (or about 49000 years). This r educes the reliability of the inference of population affinities to a historical, rather than evolutionary time scale. This is best illustra ted by the construction of a human evolutionary tree based on chromoso me Y STRs in which most of the branches connect in a markedly differen t way compared with trees based on classical protein polymorphisms and /or mtDNA sequence variation. Thus, the chromosome Y STRs seem to be v ery useful in comparing closely related populations which cannot proba bly be separated by e.g. autosomal STRs. However, in order to be used in an evolutionary context they need to be combined with more stable Y -polymorphisms e.g.; base-substitutions.