Genomic analysis links modern Indians to two ancestral populations

In a study published in the September 24th issue of Nature, an international team describes how they harnessed modern genomic technology to explore the ancient history of India, the world's second most populous nation.

The new research reveals that nearly all Indians carry genomic contributions from two distinct ancestral populations. Following this ancient mixture, many groups experienced periods of genetic isolation from each other for thousands of years. The study, which has medical implications for people of Indian descent, was led by scientists at the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad, India together with US researchers at Harvard Medical School, the Harvard School of Public Health and the Broad Institute of Harvard and MIT.

"This work is an outstanding example of the power of international collaboration," said Lalji Singh, senior author of the Nature paper, who is a Bhatnagar Fellow and the former director of CCMB. "Scientists in India and the United States have together made discoveries that would have been impossible for either group working alone."

Although the genome sequences of any two unrelated people differ by just 0.1%, that tiny slice of genetic material is a rich source of information. It provides clues that can help reconstruct the historical origins of modern populations. It also points to genetic variations that heighten the risk of certain diseases. In recent years, maps of human genetic variation have opened a window onto the diversity of populations across the world, yet India has been largely unrepresented until now.

To shed light on genetic variability across the Indian subcontinent, the research team analyzed more than 500,000 genetic markers across the genomes of 132 individuals from 25 diverse groups, representing 13 states, all six language families, traditionally "upper" and "lower" castes, and tribal groups.

These genomic analyses revealed two ancestral populations. "Different Indian groups have inherited forty to eighty percent of their ancestry from a population that we call the Ancestral North Indians who are related to western Eurasians, and the rest from the Ancestral South Indians, who are not related to any group outside India," said co-author David Reich, an associate professor of genetics at Harvard Medical School and an associate member of the Broad Institute of Harvard and MIT.