December 24, 2008
By Syed Akbar
Hyderabad, Dec 23: The paternal lineage of South Indians is traceable to Europe while their maternal genes point to East Asia.
A joint study by a group of international research organisations on the caste populations in Tamil Nadu and Andhra Pradesh has revealed that South Indian paternal lineages have been more substantially influenced by western or central Eurasians compared to South Indian maternal lineages.
The study was conducted by the Department of Human Genetics, University of Utah, USA, Schizophrenia Research Foundation, India, Queensland Centre for Mental Health Research, Australia, and University of Washington School of Medicine, USA. The researchers suggested an affinity between Dravidian populations from South India
and populations in the north and west.
The research team led by senior scientist Dr LB Jorde studied Y-chromosomes (for paternal lineage) and found that Tamil castes showed higher affinity to Europeans than to eastern Asians, and that genetic distance estimates to the Europeans are ordered by caste rank.
And when the team studied the mitochondrial DNA (maternal lineage), it found that Tamil castes have higher affinity to eastern Asians than to Europeans. Same was the case with caste populations in Andhra Pradesh.
Certain South Asian lineages are common in Tamil and Andhra castes. One of the South Asian lineages, U7, is the most prevalent "U" lineage in both the groups. Interestingly, U7 is also common in Iran, Pakistan, and northern India. "This suggests an affinity between Dravidian populations from South India and populations to the north and west," Dr Jorde said.
Although other interpretations may be possible, Dr Jorde said their data from the research study is "consistent with a model in which nomadic populations from northwest and central Eurasia intercalated over millennia into an already complex, genetically diverse set of subcontinental populations."
As these populations grew, mixed, and expanded, a system of social stratification likely developed in situ, spreading to the Indo-Gangetic plain, and then southward over the Deccan plateau. The predominantly south and east Asian mtDNA (maternal) haplogroup M is found in more than half of individuals from a wide sampling of castes and is nearly fixed in some AustroAsiatic tribal populations. This maternal
haplogroup is uncommon in western European populations.
In contrast, some paternally-inherited Y-chromosome lineages are more closely related to lineages originating in central Asians and Europeans.Genetic distances estimated from autosomal polymorphisms have typically demonstrated that caste populations tend to occupy a position intermediate between European and East Asian populations.
"The genetic affinities among the more than 2000 extant caste populations of India, however, are complex. Genetic distances between caste populations from Andhra Pradesh are correlated with differences in caste rank, suggesting that endogamy and differential inter-caste gene flow influences genetic structure," the study noted.
The study reveals that in Tamil Nadu, genetic distances between castes are positively correlated with caste rank. A similar pattern was detected in upper, middle, and lower rank castes of Andhra Pradesh.
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