Y Chromosome, Mtdna Polymorphisms And The East Asian Population Genetic Structure

Although the "Out-of-Africa" hypothesis of modern human origin has been supported extensively by genetic and archaeological evidences, the scenario of colonization of East Asia remain unclear. Genetic data provide some indication that the spread of humans into East Asia probably occurred through two roads: the first was along the coast to south and southeast Asia (the southern road), and the other was through the Middle East to Central Asia (the northern road). To reveal the relative contributions of the two roads to East Asian gene pools, variation of 5131 Y chromosomes from 120 East Asian populations and 4238 mtDNAs from 101 populations was analyzed. By considering of world-wide distribution of haplogroups and by comparing of gene diversity, it was deduced that the Y chromosome haplogourp O-M175, C-M130, D-YAP and mtDNA lineage B, R9 and M were the southern-road components, which account for 80% and 85% of the paternal and maternal gene pools of East Asian, respectively. Contrarily, the northern-road lineages encompassed only 9% and 1.2% of East Asian Y chromosome and mtDNA. Thus, the peopling of East Asians mainly involved the southern road migration. A markedly genetic difference of northern and southern East Asians was revealed by the haplogroup distributions of both Y chromosome and mtDNA as well as principal component analysis and AMOVA. And the result of autocorrelation analysis further indicated a south-north cline in East Asia. By integration the evidences of genetics and other fields, the author concluded that the south-to-north migration and subsequently multiple expansion in southern and northern East Asia is the major factor led to this distinction. A higher existence of early northern-road components in northern East Asia further increased the difference of northern and southern East Asians. However, possible influence of natural selection was not fully excluded, and further investigation is needed. Based on the estimation of "molecular clock", 20,000 years might be the upper limit of north-south differentiation, and 18,000 to 11,000 years ago was probably the most important period to form this distinction. During the past thousands of years, the second wave of northern-road migration enhanced the difference, while the north-to-south expansion of Sino-Tibetan populations balanced this distinction to some extent.The coevolution of Y chromosome and language was observed in East Asians, but there was little correlation between mtDNA variation and linguistic classification. This indicated that the word "Father tongue" is a more appropriate description of the relationship of gene and language evolution in East Asian. The extent of Y chromosome differentiation was much larger than that of mtDNA, supporting a higher migration rate of female than male in East Asia. Furthermore, this dissertation provided evidence for a general south/north admixture, and more interestingly, a stronger influence of northern immigrants on the male lineages and the southern natives contributes more extensively to the female lineages in the southern Tibeto-Burman and southern Han populations, which was initially lived in northern China and moved to the south in the past 2.5 thousands of years. And this might be attribute to the higher female migration rate in East Asians.