Tuesday, May 23, 2006

Population subdivision in Indian subcastes

Genetic diversity within a caste population of India as measured by Y-chromosome haplogroups and haplotypes: Subcastes of the Golla of Andhra Pradesh

R. J. Mitchell, B. M. Reddy, D. Campo, T. Infantino, M. Kaps, M.H. Crawford

AJPA: July, 2006, 130:385-393

The extent of population subdivision based on 15 Y-chromosome polymorphisms was studied in seven subcastes of the Golla (Karnam, Pokanati, Erra, Doddi, Punugu, Puja, and Kurava), who inhabit the Chittoor district of southern Andhra Pradesh, India. These Golla subcastes are traditionally pastoralists, culturally homogeneous and endogamous. DNA samples from 146 Golla males were scored for seven unique event polymorphisms (UEPs) and eight microsatellites, permitting allocation of each into haplogroups and haplotypes, respectively. Genetic diversity (D) was high (range, 0.9048-0.9921), and most of the genetic variance (>91%) was explained by intrapopulation differences. Median-joining network analysis of microsatellite haplotypes demonstrated an absence of any structure according to subcaste affiliation. Superimposition of UEPs on this phylogeny, however, did create some distinct clusters, indicating congruence between haplotype and haplogroup phylogenies. Our results suggest many male ancestors for the Golla as well as for each of the subcastes. Genetic distances among the seven subcastes, based on autosomal markers (short tandem repeats and human leukocyte antigens) as well as those on the chromosome Y, indicate that the Kurava may not be a true subcaste of the Golla. Although this finding is based on a very small Kurava sample, it is in accordance with ethnohistorical accounts related by community elders. The Punugu was the first to hive off the main Golla group, and the most recently separated subcastes (Karnam, Erra, Doddi, and Pokanati) fissioned from the Puja. This phylogeny receives support from the analysis of autosomal microsatellites as well as HLA loci in the same samples. In particular, there is a significant correlation (r = 0.8569; P = 0.0097) between Y-chromosome- and autosomal STR-based distances.

some notes:
- concordance between population subdivision based on Y-chromosome analysis and population subdivision based on perceptions of elders is mixed.
- some controversy as to when the Indian caste system originated
- this population practices consanguineous marriage and village endogamy (so, no male or female biased dispersion, I guess?)
-TMRCA of these Y-chromosomes is 34, 370, lending some support to the hypothesis that the caste system originated earlier than some think.

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