Genetic Diversity and Population Structure Among 13 Endogamous Populations of Purnia, Bihar

Abstract

The relation between populations structure variables and regional diversity was investigated among the thirteen endogamous populations of Puria division, Bihar, who belonged to different castes and ethnic groups with various migratory origins The phenotypic and gene frequencies of four common loci (ABO, Rh, PTC and Color Blindness) show wide differences between populations. In general B is more common than A, but in four populations, where group O is predominant. Rh negative frequency is the highest among Brahmin and non-taster gene frequency is the least among Chamars. Among the castes, Brahmins show a maximum value of the average heterozygosity per locus (37.6%). The extent of genetic differentiation between populations (as measured by Gst) is 1.45%. The genetic distance analysis and the cluster analysis based on Nei's and Harpending and Jenkins' measure, show agreement between the observed levels of genetic diversity in line with the ethno-historical migration. This is also in agreement with the caste hierarchical structure of the regional populations. Principal component analysis based on similarity index ahows the same pattern. The apportionment of genetic diversity analysis supports the hypothesis of differential migratory origins for these populations. The Harpending and Ward model used to investigate the association between population structure and genetic diversity fits the data in predicting the heterozygosity levels in relation to the long range gene flow, especially from the eastern migrants. Introduction Understanding the extent and pattern of genetic variation and explaining the plausible causative factors among human populations are the major objectives of anthropological genetics. Previous studies have approached the problem by model-free methods, which attempt to infer possible influence of population structure variables by distance measures and dendrograms by comparing the variation between populations. Recently model-bound methods have been developed for using polygenic quantitative traits to test the hypothesis of population structure variables (especially for gene flow) on the between-population variation and genetic distance measures (Chakroborty, 1990). The application of model-based studies in some populations have revealed the extent of the influence of migration and other factors on the genetic differentiation between populations, as for example, among the Jirels of Nepal (Williams-- Blangero, 1990). In this study the model-bound approach has been considered among regional populations of known historical migration background to detect the influence of migration on the genetic differentiation. Studies among Indian populations are mostly based on model-- free methods. And the results of these studies have shown wide genetic diversity characterized by gradients of gene frequencies with uneven distribution of very high or Low frequency of a few characters in certain populations (Malhotra and Vasulu, 1993: Majumder and Mukherjee, 1993 and etc.). Attempts to explain the causative factors of this uneven pattern of distribution have shown that geographical contiguity and ethno-historical factors are the primary explanatory variables, although other associated population structure variables also play an important role. However, the relative importance of these explanatory variables differ between populations, so that to discern a general trend, studies covering many populaitons over a region and small scale local studies, especially specific populations, are necessary. In this context, regional level studies aiming to discern the genetic diversity at the level of local populations (e.g. tribal, ethnic or isolated) is expected to provide a better explanation of the causative factors involved. Indeed such regional studies in some specific populations have revealed the role of population structure in explaining the pattern of genetic variation. For example, the pattern of affinity between the two neighboring populations of Himachal Pradesh, especially, Kamte and Kotis, are due to admixture with the neighboring Tibetans (Papiha, 1985). …