Distribution of haplotypes from a chromosome 21 region distinguishes multiple prehistoric human migrations

Abstract

Despite mounting genetic evidence implicating a recent origin of modern humans, the elucidation of early migratory gene-flow episodes remains incomplete. Geographic distribution of haplotypes may show traces of ancestral migrations. However, such evolutionary signatures can be erased easily by recombination and mutational perturbations. A 565-bp chromosome 21 region near the MX1 gene, which contains nine sites frequently polymorphic in human populations, has been found. It is unaffected by recombination and recurrent mutation and thus reflects only migratory history, genetic drift, and possibly selection. Geographic distribution of contemporary haplotypes implies distinctive prehistoric human migrations: one to Oceania, one to Asia and subsequently to America, and a third one predominantly to Europe. The findings with chromosome 21 are confirmed by independent evidence from a Y chromosome phylogeny. Loci of this type will help to decipher the evolutionary history of modern humans.

Figure 1

Phylogenetic relationship among haplotypes. The arrows indicate the direction of the mutations (hollow letters). The phylogeny includes all equally parsimonious topologies by allowing multifurcation. All sites are congruent to each other, indicating the lack of recombination and recurrent mutation events within the 565-bp fragment encompassing 12 polymorphic sites in hominoids. Chimpanzee and gorilla sequences were used to determine the root of the phylogeny as well as the ancestral state of the sequences.

Figure 2

Entropies of subcontinents relative to the maximum value they can take for the two systems of haplotypes of MX1 (abscissa) and Y chromosome (ordinate) given in Tables 1 and 2. Standard errors indicated by horizontal and vertical segments are calculated by the bootstrap method.