Western Population Genetic Mixed

The ethnic groups in China are distributed unevenly, with most Han Chinese in the east and very diverse minority ethnic groups in the west. Populations from different regions of Eurasia arrived in the West China and admixed into the present populations. To reveal and assess the population origins and the admixture process, studies from both history and genetics are essential.With the advancement of molecular biology, various genetic markers have been successfully applied in population study. In order to investigate the populaiton genetic structure, analyses of Y chromosome and autosomal single nucleotide polymorphism markers were performed in 2909 individuals from nine ethnic groups in Western China.In northwest China, we selected 1514 male samples and performed high-resolution genotyping with biallic markers selected according to the Y chromosome phylogeny. Four Y Chomosome hapologroups C, D, O, and N, accounted for 64.36% of the northwest China. These haplogroups are suggested to have a Southeast Asian orgin. Their high frequencies in northwest China indicates that the substantial contribution of the southern route out of Africa. The distributions of western Eurasia specific Y chromosome haplogroups E, F, G, H, I, and J in northwest China reflect the gene flow from the west. A west-to-east decline of these western haplogroups was also observed. The northwest China people, mostly Altaic-speaking populations, were discrete in principal component plot, indicating that Altaic-speaking populations do not have genetic affinity with each other.In the southwest China, the eastern Himalayas are located near the southern entrance through which early modern humans spread into East Asia. The genetic structure in this region is therefore of great importance in the study of East Asian origins. However, few genetic studies have been performed on the Sino-Tibetan populations (e.g. Luoba and Deng) in this region. We analyzed the Y chromosome diversity of the two populations. The Luoba possessed haplogroups D, N, O, J, Q, and R, indicating gene flow from the Tibetans, as well as the western and northern Eurasians. The Deng exhibited haplogroups C, D, N, and O, similar to most Sino-Tibetan populations in the east. We further analyzed STR diversity within haplogroup O3, which is the dominant lineage in Sino-Tibetan populations. Cluster analyses showed that the Luoba are genetically closest to Tibetans and the Deng are closer to the Qiang, comparing with the other populations examined in this study. The average genetic diversity revealed that the Qiang had the greatest diversity of Sino-Tibetan populations, supporting the view of this population being the oldest in the family. The lowest diversity occurred in the eastern Himalayas, suggesting that this area was an endpoint for the expansion of Sino-Tibetan speaking groups. Thus, we have shown that populations with haplogroup 03 moved into the eastern Himalayas through at least two routes, and admixed with other populations with other haplogroups subsequently.During human migration out of Africa, the genetic structures of populations always change greatly. These changes may occur randomly along with the population dispersal or specifically according to the adaption to the regional environment. A typical example for random change is the Y chromosome diversification, and a typical example for adaptive change is the human alcohol dehydrogenase gene (ADH) diversification. Studies on the genetic markers with adaptive changes will be most helpful in understanding the emergence of the biophysical differences between the relative populations. Here, the most typical relative populations with apparent biophysical differences, Han Chinese and Tibetans, were studied by analyzing the ADH diversities.The human ADH gene family has seven members, among which ADH1B gene has been proved to be associated to many serious diseases. The derived allele of the non-synonymous polymorphism, ADH1B*47His, reaches high frequency only in East Asia and Southwest Asia. Micro-evolutionary study defined seven haplogroups for ADH IB, H1-H7. H6 and H7 are haplogroups with the ADH1B*47His. H7 is the dominant haplogroup of Han Chinese. We typed 22 SNPs in region covering ADH gene among 1175 individuals of 12 Tibetan populations from all districts of the Tibet Autonomous Region. The major populations of the Tibetans (Qamdo, Lhasa, Nagqu, Nyingchi, Shannan, and Shigatse) have around 12% of H7 and 2% of H6. Both frequencies are much lower than those in Han Chinese, but almost the same ratio between the two haplogroup frequencies. The minor populations have even lower frequencies. Long range haplotype analyses revealed very weak positive selection signals for H7 among the Tibetans. The haplotype diversity of H7 is much higher in the Tibetans than in any other populations studied, indicating a longest diversification history of the haplogroup in the Tibetans. Network analysis on the long range haplotypes revealed that H7 in the Han Chinese could not have derived from the Tibetans but from a common ancestor of the two populations. In conclusion, we argued that H7 of ADH1B originated in the ancestor of Sino-Tibetan populations and flowed to the Tibetans very early. However, as the Tibetans have only a relative short history of agriculture, selection should have only laid weak effects, and the frequency of H7 has not risen to high, whereas the diversity of the gene has accumulated to very high level.