Antiquity, geographic contiguity and genetic affinity among Tibeto-Burman populations of India: a microsatellite study.

BACKGROUND The Tibeto-Burman (TB) populations are one of the four major linguistic population groups of India. They are considered belonging to different stocks and show wide variation in culture and language; however, their genetic relationship, antiquity and migration history among the regional populations has been little investigated. Molecular genetic studies are expected to clearly show the antiquity and genetic diversity of these populations. AIM This paper seeks to understand the extent and magnitude of genetic affinities and diversities among 14 TB populations (12 Indian and two global groups), investigate the findings based on classical genetic markers and verify the historical accounts of their migration and genetic history based on 12 microsatellite markers. SUBJECTS AND METHODS The allele frequency data for 12 STR loci of 13 Asian (Tibeto-Burman) populations were obtained from the literature and the Adi Pasi data was obtained by microsatellite typing of their blood samples. The 12 loci studied are D5S818, FGA, D8S1179, D21S11, D7S820, CSF1PO, D3S1358, THO1, D13S317, vWa, TPOX, D18S51. Three different distance measures, two phylogenetic trees and PCA plot have been employed to understand the genetic relationship of the studied populations. RESULTS Average heterozygosity values range from 68 to 79% and the average G(ST) value is 4.7%. The dendrogram, based on the D(A) distance, shows the clustering of populations based on their diversities and geographical contiguity; the Mizoram and Arunachal Pradesh populations especially cluster together, populations from Sikkim form a separate subcluster and Manipur populations along with the Garo of West Bengal separate out from the other clusters. The Harpending and Ward regression model shows isolated populations positioned below the regression line and others, who experience external gene flow, placed above the line. The results support folklore migration accounts of their possible antiquity with the Tibetan and southern Chinese populations. CONCLUSIONS Overall, geographic contiguity, punctuated by isolating barriers, is a major influencing factor of genetic affinity among the TB population; contiguous populations within a region show greater genetic relationship than with distant TB populations over a wide geographical area. The results of the microsatellite study also support the history of diverse routes of migration of these populations.