"Although India comprises more than one sixth of the world's human population, it has largely been omitted from genomic surveys that provide the backdrop for association studies of genetic disease." So begin Noah Rosenberg et al. in PLoS Genetics. They analyzed 1,200 genome-wide polymorphisms in 432 individuals from 15 Indian populations - all Indian-born but residing in the United States. They conclude:
Populations from India, and groups from South Asia more generally, form a genetic cluster, so that individuals placed within this cluster are more genetically similar to each other than to individuals outside the cluster. However, the amount of genetic differentiation among Indian populations is relatively small. ...Genetic variation in India is distinctive with respect to the rest of the world, but...the level of genetic divergence is smaller in Indians than might be expected for such a geographically and linguistically diverse group.