Spatial and temporal distribution of the neutral polymorphisms in the lastZFX intron: Analysis of the haplotype structure and genealogy

With 10 segregating sites (simple nucleotide polymorphisms) in the last int ron (1089 bp) of the ZFX gene we have observed 11 haplotypes in 336 chromos omes representing a worldwide array of 15 human populations. Two haplotypes representing 77% of all chromosomes were distributed almost evenly among f our continents. Five of the remaining haplotypes were detected in Africa an d 4 others were restricted to Eurasia and the Americas. Using the informati on about the ancestral state of the segregating positions (inferred from hu man-great ape comparisons), we applied coalescent analysis to estimate the age of the polymorphisms and the resulting haplotypes. The oldest haplotype , with the ancestral alleles at all the sites, was observed at low frequenc y only in two groups of African origin. Its estimated age of 740 to 1100 ky r corresponded to the time to the most recent common ancestor. The two most frequent worldwide distributed haplotypes were estimated at 550 to 840 and 260 to 400 kyr, respectively, while the age of the continentally restricte d polymorphisms was 120 to 180 kyr and smaller. Comparison of spatial and t emporal distribution of the ZFX haplotypes suggests chat modern humans dive rged from the common ancestral stock ill the Middle Paleolithic era. Subseq uent range expansion prevented substantial gene flow among continents, sepa rating African groups from populations that colonized Eurasia and the New W orld.