Trading genes along the silk road: mtDNA sequences and the origin of central Asian populations

Central Asia is a vast region at the crossroads of different habitats, cult ures, and trade routes. Little is known about the genetics and the history of the population of this region. We present the analysis of mtDNA control- region sequences in samples of the Kazakh, the Uighurs, the lowland Kirghiz , and the highland Kirghiz, which we have used to address both the populati on history of the region and the possible selective pressures that high alt itude has on mtDNA genes. Central Asian mtDNA sequences present features in termediate between European and eastern Asian sequences, in several paramet ers-such as the frequencies of certain nucleotides, the levels of nudeotide diversity, mean pairwise differences, and genetic distances. Several hypot heses could explain the intermediate position of central Asia between Europ e and eastern Asia, but the most plausible would involve extensive levels o f admixture between Europeans and eastern Asians in central Asia, possibly enhanced during the Silk Road trade and clearly after the eastern and weste rn Eurasian human groups had diverged. Lowland and highland Kirghiz mtDNA s equences are very similar, and the analysis of molecular variance has revea led that the fraction of mitochondrial genetic variance due to altitude is not significantly different from zero. Thus, it seems unlikely that altitud e has exerted a major selective pressure on mitochondrial genes in central Asian populations.