Genetic profile based upon 15 microsatellites of four caste
Genetic profile based upon 15 microsatellites of four caste groups of the eastern Indian state, Bihar
R Asma and V.K Kashyap,
Since microsatellite markers are more informative than classical serological and other protein markers, in the current study, 15 microsatellite markers present in the Combined DNA Index System (CODIS), validated for the population of India, were chosen to estimate the impact of the deep-seated man-made caste system on the gene flow among four socio-culturally predominant caste groups(Brahmin, Bhumihar, Rajput and Kayasth) of Bihar. The chosen social groups share a common geographical area, socio-cultural practices and language that could result in high gene flow among them, due to the intrinsic drive to reproduce. An attempt has been made to understand the existing affinity due to inter-caste geneflow and relative diversity due to the high degree of endogamy practiced at the caste level. This is perhaps the first genetic study based upon 15 short tandem repeat(STR) loci to understand the impact of the caste system on human gene pool.
Subjects and methods
The populations In Bihar, the majority of people practices Hinduism and follows the caste system, hierarchically organized into upper, middle and lower strata. Social orders selected for the present study occupy the upper strata and are the major and dominant castes of the state having Caucasian features. Predominantly, they speak the Bhojpuri or Maithli dialect that belongs to the Indo-European linguistic family—the major contributor to the development of Indian culture and society (Meenakshi 1995).The mainstay of their food habit is identical, consisting of wheat and rice. Their regional deities are also similar and they celebrate the same festivals. Brahmin occupy the top slot in the Hindu society, having 186 sub-castes distributed in as many as 12 states and union territories, with historical accounts of extensive migration, mostly from the upper Gangetic region to the other parts of the country. There is a striking range of diversities in terms of morphology and genetic traits, though they strictly observe endogamy at the community level (>90%)(Singh 1998). Bhumihar (the third largest category of Brahmins) was attempted to be declassified by the Brahmins during the late 19th century, owing to their occupation as agriculturists, and was placed below Brahmin. Perhaps, because of the use of surnames such as Mishra, Tiwari, Chaudhary, Singh, Thakur, etc., by Bhumihar, which are common among Brahmin as well as in Rajput, their status in the Hindu caste system is a matter of controversy. Rajput constituted the most heterogeneous community of traditional warriors, rulers, landlords, peasants and even workers, and was more numerous in Uttar Pradesh, followed by Punjab and Bihar. Major clans of the Rajput are spread over 110 districts in the country.
Pairwise genetic distance (DA) between the populations clearly demonstrates that Bhumihar is closer to Brahmin (0.0298)than Rajput (0.035) or Kayasth (0.0653). Again, Rajput is closer to Bhumihar(0.032) than Brahmin (0.035) and Kayasth (0.0683), i.e. the position of Bhumihar lies somewhere between Brahmins and Rajput, while Kayasth comes after Rajput
the Brahmin has relatively high rii value(1.52 x 10 power -4) but has the lowest value of average heterozygosity (0.739), and lies below the regression line, indicating that Brahmin practices high endogamy and has lesser gene flow than the rest of the three groups, i.e. the Brahmin community is still under extreme reproductive isolation from the rest of the advanced caste groups of the state.
Like Brahmin, Bhumihar is also below the regression line but has a high average heterozygosity value (0.757) and low rii value(0.26 x10 power -4), demonstrating reasonable amount of gene flow.
Rajput has low average heterozygosity (0.742) like Brahmin but also has low rii values (0.23 x10-4), situated below the regression line that portrays them as an endogamous community. Kayasth has a high value of rii (0.37 x10-4) com-pared with Bhumihar and Rajput. Level of average heterozygosity (0.782) is also highest and the community is above the regression line depicting very high gene flow, which may be on account of their traditional occupation as accountants in the past. Kayasth had a very close interaction with poor villagers who were not able to paytheir tax. Since there was a system of bonded labour in the state and Kayasth is among the dominant group, they may have reproductively exploited the low caste groups.
