Genetic differentiation of Andaman Islanders and their relatedness to Nicobar Islanders

Abstract

The Andaman Islanders, living in isolation for centuries, have been subject to recent molecular scrutiny with their Asian origins being established. Although marked linguistic and physical variations are known to exist among the different extant population groups, the underlying genetic structure with reference to indigenous populations of adjacent Nicobar Islands has been poorly understood. To decipher the genetic structure of three indigenous Andaman Islanders; the Great Andamanese, Jarawa and the Onge, molecular analyses with autosomal, mitochondrial and Y-chromosomal markers were carried out and compared with indigenous Nicobar Islanders; the Nicobarese and Shompen.Biparental analyses revealed the Great Andamanese exhibiting considerable population substructuring owing to their present-day conglomeration of several erstwhile segregate tribes, in addition to discernable admixture from mainland Indian populations and other Andaman and Nicobar Islanders especially the Nicobarese. Distant separation between the Great Andamanese and Nicobarese was also discerned by the shared R22 mitochondrial lineage. The R22 lineage was previously reported in the Shompen of Nicobar Islands and Southeast Asian populations. The Nicobarese also exhibited mitochondrial haplogroup M74b, which has a Southeast Asian and East Asian distribution.The Onge-Jarawa group demonstrated a close genetic relatedness, consistent with their linguistic proximity. However, recent differentiation of the Jarawa from the Onge was also inferred from their separation on both mitochondrial M31 and M32 lineages as well as from autosomal and Y-chromosomal divergences. Our analyses indicate considerable genetic drift among the Andaman Islanders, a result of long-term isolation and inbreeding.Autosomal and mitochondrial data suggest considerable admixture between the ‘Negrito’ Great Andamanese and ‘non-Negrito’ Nicobarese.