Polymorphisms of the human Y chromosome: Applications in identity tests and human evolution

Abstract

In this investigation, a broad study was done using two polymorphic systems detected by PCR in the human Y chromosome: the microsatellite polymorphism in the locus DYS19 and the polymorphic ah system detected by heteroduplex analysis. The molecular basis of the ah system was thoroughly investigated revealing the origin of the polymorphic heteroduplexes. Four new alleles were described in the DYS19 locus and 22 haplotypes for the ah system resulted from different combinations of 17 heteroduplex pairs were characterized. The investigation of both polymorphisms allowed to be evaluated their usefulness for identity tests (paternity and forensic tests) and human evolutionary studies. It was shown that an individual from the Brazilian population can be differentiated from another with an average chance of 82%, a high identification index using only these two polymorphic systems. In the worldwide population at least 46 Y chromosomes could be discriminated by using ah and DYS19. Different types of Y chromosomes appeared in each ethnic group and some ah haplotypes were suggested to be used as marker of particular populations. The DYS19 locus displayed a multiple origin of its alleles but in a lower scale than autosomal ones, thus more useful for evolutionary studies. Among Amerindians we found a highly frequent Y chromosome considered here as the major founder haplotype of the American aboriginal populations and also two other possible minor founder haplotypes were seen in brazilian amerindians from the amazon basin with a very low detected admixture. The study of the 46 patrilineages compared to YAP Alu insertion polymorphism, and also the knowledge of the molecular basis for generation of the ah polymorphism allowed us to draw an informative evolutionary picture of these patrilineages which confirmed the African origin of the Alu insertion. The comparison of these patrilineages with other Y haplotypes studied in other laboratories in the same samples displayed the single origin of most ot the ah haplotypes and their usefulness for evolutionary approaches.