Mitochondrial DNA variation of tai speaking peoples in Northern Thailand

Abstract

The genetic structure and genetic affinity of Tai ethnic populations in northern Thailand has never been investigated, therefore their biological ancestor as well as their history is not clearly resolved. In this study, we examined the D-loop fragment of the mitochondrial DNA in 496 unrelated individuals belonging to 4 Tai ethnic groups from 10 villages: 4 Yuan, 4 Lue, 1 Yong and 1 Khuen. Based on a comparison of 522bp sequences at the position 16048-16569, 195 distinct haplotypes defined by 130 polymorphic sites were distinguished. Of these, 154 types were unique to their respective populations, whereas 41 were shared by two or more populations, The studied Tai populations showed evidence of demographic expansion with corresponding estimated expansion times of more than 66.000 years before the present. During historical migration and settlement, intensive genetic drift and founder effects left their imprint as population differentiation. Genetic affinity among the populations was not consistent with their linguistic classification. The Yuan or Khon Muang in northern Thailand exhibited a close relationship to the Tai groups in South and Southeast China, which supported the immigrant hypothesis and their ancestor's origin. However, an admixture between the Khon Muang and the Lawa and Mon, the long existing populations of northern Thailand, needs to be investigated.