The Y Alu polymorphism in southern African populations and its relationship to other Y-specific polymorphisms.

Y-linked polymorphisms were studied in a number of African populations. The frequency of the alleles of a Y-specific Alu insertion polymorphism, termed the "Y Alu polymorphism," was determined in 889 individuals from 23 different African population groups. A trend in frequency was observed, with the insert largely absent in Caucasoid populations, at intermediate frequency in the Khoisan, and at high frequency in Negroids. The insert predates diversification of Homo sapiens, since it occurs in all groups. The Alu insertion is believed to result from a unique mutation event, and comparisons between this and several other Y-linked polymorphisms were carried out in an attempt to validate their usefulness in population and evolutionary studies. The p21A1/TaqI and pDP31/EcoRI polymorphisms and 49a/TaqI alleles were all shown to have arisen on more than one occasion, and evidence exists for a preraciation crossover event between the Y-linked pseudoautosomal XY275 locus and the Y chromosome pseudoautosomal boundary.