Indian ancestry revealed

[FarCenter]

The mixing of two distinct lineages led to most modern-day Indians.

Elie Dolgin

Most Indians are a mix of two ancient lineages.GettyThe population of India was founded on two ancient groups that are as genetically distinct from each other as they are from other Asians, according to the largest DNA survey of Indian heritage to date. Nowadays, however, most Indians are a genetic hotchpotch of both ancestries, despite the populous nation's highly stratified social structure.

"All Indians are pretty similar," says Chris Tyler-Smith, a genome researcher at the Wellcome Trust Sanger Institute near Cambridge, UK, who was not involved in the study. "The population subdivision has not had a dominating effect."

India makes up around one-sixth of the world's population, yet the South Asian country has been sorely under-represented in genome-wide studies of human genetic variation. The International HapMap Project, for example, includes populations with African, East Asian and European ancestry — but no Indians. The closest the Human Genome Diversity Cell Line Panel of 51 global populations comes is Pakistan, India's western neighbour. The Indian Genome Variation database was launched in 2003 to fill the gap, but so far the project has studied only 420 DNA-letter differences, called single nucleotide polymorphisms (SNPs), in 75 genes1.

Caste divisions

Now, a team led by David Reich of the Broad Institute in Cambridge, Massachusetts, and Lalji Singh of the Centre for Cellular and Molecular Biology in Hyderabad, India, has probed more than 560,000 SNPs across the genomes of 132 Indian individuals from 25 diverse ethnic and tribal groups dotted all over India.

The researchers showed that most Indian populations are genetic admixtures of two ancient, genetically divergent groups, which each contributed around 40-60% of the DNA to most present-day populations. One ancestral lineage — which is genetically similar to Middle Eastern, Central Asian and European populations — was higher in upper-caste individuals and speakers of Indo-European languages such as Hindi, the researchers found. The other lineage was not close to any group outside the subcontinent, and was most common in people indigenous to the Andaman Islands, a remote archipelago in the Bay of Bengal.

The researchers also found that Indian populations were much more highly subdivided than European populations. But whereas European ancestry is mostly carved up by geography, Indian segregation was driven largely by caste. "There are populations that have lived in the same town and same village for thousands of years without exchanging genes," says Reich.

<SNIP> Story continues at http://www.nature.com/news/2009/090922/full/news.2009.935.html

[hedgehog]

1. Pretty much corresponds to what I've always thought.