Social structure defined by the caste system has a "profound" influence on skin pigmentation, according to a study conducted by the city-based Centre for Cellular and Molecular Biology (CCMB).
The study was carried out in collaboration with Estonian Biocentre, Estonia, on skin colour of over 1,000 individuals in India. It has explored the genetics of skin colour variations across the country.
The findings also reflected the "profound influence" of the strict marriage patterns and multi-layered endogamy adding further to the variation in skin colour.
The study, led by Kumarasamy Thangaraj, the senior principal scientist at CCMB, Estonian Biocentre, and five other institutes was published on November 17 in the online edition of the Journal of Investigative Dermatology.
"We have done extensive epidemiological survey of 1,167 individuals belonging to 27 populations and quantified melanin content at most exposed and low exposed area of human body at Middle region of Gangatic plains (Uttar Pradesh and Bihar), and selected 374 individuals for the first round of genetic study," a CCMB release issued today quoted Anshuman Mishra, the first author of the study, as saying.
The researchers said SLC24A5 gene is known to make skin lighter and explains about 25-38 per cent of pigmentation differences between Europeans and West Africans.
A variant/modification (rs1426654) in the gene has been earlier shown to be associated with skin pigmentation measures in India, the release stated.
In this study, the research team has analysed the entire gene and found another variant (rs2470102), which contributes to skin pigmentation variation in Indian subcontinent.
"Further analyses revealed that both the variants (rs1426654 and rs2470102) together could better explain the variation in skin colour among Indian populations than considering each variant independently.
"The difference in skin colour persisted even when the contribution by the previously known SNP (single nucleotide polymorphism) was adjusted, suggests that the new SNP has an independent effect on skin colour," it said.
The authors found that social structure defined by the caste system has a "profound influence on skin pigmentation.
The authors found out that skin colour was found to vary
significantly among ethnic groups and social categories studied. The researchers then compared the skin colour (phenotype) with the genetic variation (genotype) of the individuals. Those with derived (mutant) alleles had fairer skin compared to those who had old (wild type) alleles.
"Our study clearly reflects the profound influence of the strict marriage patterns and multi-layered endogamy adding further to the variation in skin colour contributing to the mosaic of skin tones," said Chandana Basu, one of the authors of the study and a researcher at Estonian Biocentre.
This team also studied 1,825 individuals belonging to 52 diverse populations across India and found that the social category and associated SNPs explain 38.4 per cent of the variation in skin color.
"Unlike Africans and Europeans, we do not have homogeneous skin colour throughout the country. This could be due to different waves of human migration into India and recent admixture of all Indian populations, which we predicted in our previous study that it could have happened about two thousand years ago," said Thangaraj.
This is yet another effort of CSIR-CCMB in the field of genomics, which helped us understand the genetic link to the skin colour, said CCMB Director Rakesh Mishra.
"These are steps that point to the era of personalised medicine based on link of genomic features with disease susceptibility and drug response.
"Such studies, at very large scales, will be needed to establish individual specific lifestyle advisory and medical prescriptions as it is clear that 'one size does not suit all' is also applicable to the area of human health and disease," Mishra added.
