Mitochondrial DNA polymorphisms in Thailand

Nucleotide sequences of the D-loop region of human mitochondrial DNA from s ix small ethnic groups of Thailand i.e., Hill tribes (Lisu and Mussur), Phu thai, Lao Song, Chong, and aboriginal Sakai, were analyzed. The sequences w ere compared with those of native Thai populations from two provinces, Chia ng Mai and Khon Kaen. Based on a comparison of the 563-bp sequences in 215 Thai individuals, 137 different sequence types were observed. Of these, 124 were unique to their respective populations, whereas 13 were shared betwee n two to five populations. The intergenic COII/tRNA(Lys) 9-bp deletion was observed in every Thai population examined, except for the Sakai, with vary ing frequencies ranging from 18% to 40%. The D-loop sequences variation, an d phylogenetic analysis, suggested that the 9-bp deletion had occurred in a very ancient ancestry of Southeast Asians, although multiple origins of th e deletion cannot be ruled out. Genetic distances, based on net nucleotide diversities, between populations revealed that the Sakai were distantly rel ated to the other Thai populations, while the Lao Song and Chong were close ly related to each other. Close genetic affinities were also observed among the Hill tribes, Phuthai, and native northeast Thai (Khon Kaen), indicatin g that they may share some degree of the common ancestral maternal lineages .