Abstract
BackgroundMajor population movements, social structure, and caste endogamy have influenced the genetic structure of Indian populations. An understanding of these influences is increasingly important as gene mapping and case-control studies are initiated in South Indian populations.ResultsWe report new data on 155 individuals from four Tamil caste populations of South India and perform comparative analyses with caste populations from the neighboring state of Andhra Pradesh. Genetic differentiation among Tamil castes is low (RST = 0.96% for 45 autosomal short tandem repeat (STR) markers), reflecting a largely common origin. Nonetheless, caste- and continent-specific patterns are evident. For 32 lineage-defining Y-chromosome SNPs, Tamil castes show higher affinity to Europeans than to eastern Asians, and genetic distance estimates to the Europeans are ordered by caste rank. For 32 lineage-defining mitochondrial SNPs and hypervariable sequence (HVS) 1, Tamil castes have higher affinity to eastern Asians than to Europeans. For 45 autosomal STRs, upper and middle rank castes show higher affinity to Europeans than do lower rank castes from either Tamil Nadu or Andhra Pradesh. Local between-caste variation (Tamil Nadu RST = 0.96%, Andhra Pradesh RST = 0.77%) exceeds the estimate of variation between these geographically separated groups (RST = 0.12%). Low, but statistically significant, correlations between caste rank distance and genetic distance are demonstrated for Tamil castes using Y-chromosome, mtDNA, and autosomal data.ConclusionGenetic data from Y-chromosome, mtDNA, and autosomal STRs are in accord with historical accounts of northwest to southeast population movements in India. The influence of ancient and historical population movements and caste social structure can be detected and replicated in South Indian caste populations from two different geographic regions.
Highlights
Major population movements, social structure, and caste endogamy have influenced the genetic structure of Indian populations
We show that the genetic affinities between Indian castes from Tamil Nadu and other Eurasians are broadly congruent with patterns observed previously for castes from Andhra Pradesh
Y-chromosome haplogroups We evaluated the genetic relationship between Tamil castes, eastern Asians, and Europeans using 32 lineagespecific Y-chromosome single nucleotide polymorphisms (SNPs)
Summary
Social structure, and caste endogamy have influenced the genetic structure of Indian populations. An understanding of these influences is increasingly important as gene mapping and case-control studies are initiated in South Indian populations. The historical record documents an influx of Vedic Indo-European-speaking immigrants into northwest India starting at least 3500 years ago [8,9,10,11]. These immigrants spread southward and eastward into an existing agrarian society dominated by Dravidian speakers [12]. The extent to which ancient and contemporary migrations, and the more recent inception of a hierarchical caste system, have influenced the genetic composition of modern Indian populations remains controversial
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