Asian or African Origin of A Homo Sapiens Paternal Lineage

Abstract

Alu repeats are short interspersed elements (SINE) with nearly 106 dispersed copies representing about 5% of the genetic material in primates. These mobile inserts have several interesting properties. First, they generate biallelic polymorphisms (absence/presence of the insert) that can be easily typed by PCR. Second, they are stable and unique in such a way that all individuals sharing the same Alu insert can be traced back to a single and common ancestor in which the insertion occurred for the first time. Third, the absence of the insert is always the ancestral state. Several Alu inserts Known to occur in humans after the human/ape divergence have been extensively used to infer the evolution of modern human populations. Among these human specific elements, one of them is particularly interesting due to its location in the non-recombinant region (DYS287 locus) of the human Y chromosome; YAP + and YAP – acronyms identify the presence of absence (ancestral state) of the insert, respectively. The Y-specific regionof Y chromosomes is haploid and is patrilineally transmitted along generatios. As this region does not undergo recombination, all Y-specific genes and markers are in linkeage disequilibrium, with mutations being the only potential source of variation between the male ancestor and his male offspring. YAP+ chromosomes appear at low frequency (＜10%) in some Asian, Oceanian, and Amerindian populations, at intermediate frequency (11-30%) in Caucasians and Japanese, and at high frequency (＞31%) in Tibetans and several African populations. All extant YAP+ chromosomes are known to derive from the Y chromosome of a single modern human in which the Alu transposition on Y occurred for the first time. Since its origin, this Alu domain accumulated several biallelic additional mutations: two C to T transitions at 338bp (PN1) and 1682bp (PN2) loci, and a deletion of the poly-. A tail (S for short tail). Finally, outside the Alu domain, two other mutations, a G to A transition at 4064bp of the SRY domain, and an A to G transition at 168bp position of the DYS271 locus were also informative. Using the above polymorphisms plus 7 microsatellite loci, we detected 60 different haplotypes distributed in 14subhaplogroups. Three of these haplotypes were shared by two individuals, one was shared by four, and one by five individuals, respectively. It is proposed that each lineage started from a single individual and then became expanded to generate, chronologically and hierarchically, the haplogroups, then the subhaplogroups, and finally the haplotypes. In some cases the ancestral and derived lineages coexist within the group while in other occasions the growth of derived haplotypes produces the partial or total replacement of ancestral lineages. These lineage losses may explain the lack of several links in the evolutive pathway of YAP+ chromosomes. Two alternative models can be used to explain the geogpraphical distribution of YAP+ chromosomes. The out-of-Asia hypothesis assumes: (a) an Asian origin for the Alu insert (haplogroup A); (b) spreading and diversification of the YAP+ elements in Africa (haplogroups B-D); and (c) suequent migration from Africa to Europe (haplogroup C). The out-of-Africa model proposes: (a) origin and diversification of YAP+ chromosomes in Africa (haplogroups A-D); and (b) migration of haplogroup A to Asia and of haplogroup C to Europe. Both models require the extinction of one haplogroup in a geographic region: haplogroup B in Asia or haplogroup A in Africa for the first model described, or haplogroup A in Africa for the second model.