Indians share same mutation for light skin as Europeans: Study

PTI| Updated: Nov 15, 2013, 17:29 PM IST

 Hyderabad: Europeans and some Indians share the same light skin gene mutation, a new study has found.

 Genetic studies done so far have helped in understanding the pigmentation genetics of Europeans to some extent, but South Asians, who represent wide range of skin colour have so far not been explored, K Thangaraj, senior lead author from the CSIR-Centre for Cellular and Molecular Biology (CCMB) here said.

The team of scientists led by researchers from University of Tartu, Estonia, CCMB and University of Cambridge have studied one of the important pigmentation genes, SLC24A5, and published their findings in PLoS Genetics, CCMB said.

 "We studied a homogeneous cohort of India and found that SLC24A5 gene explains most of the variation of the pigmentation extremes and has a major effect on pigmentation diversity," Thangaraj said.

 The study also provides the first detailed map of the genetic variant and shows that the light skin associated genetic signature is wide spread in Indian sub-continent with substantial variation among different ethnic groups, he said.

 Re-sequencing of 11.74 kb of SLC24A5 gene using a global sample set have helped the researchers to unveil an important fact that Indians share the same mutation of SLC24A5 for their light skin as Europeans and belong to the same haplotype (study of heredity and etc) background, Thangaraj said.

 "It was interesting to see that the effect of geographical, linguistic, socio-cultural boundaries further shaped by strict endogamy which forms the backbone of the South Asian genetic diversity was so strongly reflected in the complex patterning of this light skin allele (one member of a pair or series of genes that occupy a specific position on a specific chromose)," CCMB quoted Chandana Basu Mallick, first author of the study from University of Tartu, as saying.

Elaborating on the study, Thangaraj said human skin colour varies widely among populations and is a classic example of adaptive evolution.

 "Pigmentation in humans is largely determined by the quantity and distribution of the biopolymer melanin, contained within melanosomes.

 A significant correlation between skin colour and ultra-violet radiation levels observed at the global scale suggests that natural selection plays an important role in determining the distribution of this phenotypic trait," he said.

 The evolution of dark skin at low latitudes has been mainly attributed to the requirement of 'photo-protection' against sun-burn and skin cancer, whereas the evolution of light skin has been most commonly associated with vitamin D deficiency, he said.

 "When humans started moving to higher latitudes where ultraviolet radiation levels were lower, individuals with dark skin could not absorb sufficient ultraviolet radiation for efficient vitamin D synthesis and thus natural selection favoured evolution of light skin," he said.

 The study also provides the first comprehensive estimate of coalescence time of this genetic signature ranging 22-28 thousand years ago, which is crucial in the understanding of evolutionary history of light skin in humans.

 "The wide presence of the allele (alternative form of a gene) in India suggests that this allele was probably not a part of recent gene flow but existed in the sub-continent several thousand years ago," CCMB quoted Gyaneshwar Chaubey, co-author of the study.

 Apart from understanding the evolution of skin colour, the study when matured may have new insights into the proper use of cosmetics, CCMB Director Ch Mohan Rao said.