Ethnogenetic Relation of Tharu Living in Indo-Nepal Himalayan Terai (West Champaran: Bihar: India) Based on Serological Study of A 1 A 2 BO*H and Rh Blood Groups with Report of Bombay Phenotype (O h )

Background Tharu is a heterogeneous group, as its subgroups claim their origin from different lineages, and it is considered that they share ancestry with different ethnic stocks. The present paper is a preliminary report on ethnogenetic relationships on the basis of a serological study of A 1 , A 2 , B, O*H and Rh blood groups. Materials and Methods The sampling was based on a two-stage randomised cluster method carried out in Tharuat ( West Champaran ) from May 2024 to July 2024 ( N = ~384). The A 1 A 2 BO*H and Rh blood groups were determined. Both forward and reverse blood grouping methods were used for confirmation of Bombay phenotype. The allele frequencies and genotypes were calculated for both primary and secondary data by Bernstein’s method. The X ² test was used for determination of significance level. The values of Nei’s gene diversity index, Genetic distance matrix (D) and dendrogram were used for the determination of ethnogenetic relationship. Results The percentage prevalence of A 1 (21.67), A 2 (0.0), B (38.65), O (28.19), A 1 B (11.49) and A 2 B (0.0) represented no statistically significant deviation from expected values ( χ ² = 0.7053, df = 4, p > .05). The allele frequencies were observed as 0.18(I A1 ), 0.29(I B ), 0.53(I O ) and 0.0(I A2 ). The observed percentage of Rh-negative was 1.58 ( q = 0.13) also represented no statistically significant deviation from expected values ( χ ² = 0.000437, df = 1, p > .05). The H_ and hh of the O phenotype were 99.48% ( p = .93) and 0.52% ( q = .07), respectively ( χ ² = 0.000036, df = 1, 1 > p > .99, non-significant). The different components of Nei’s gene diversity (H T (Total gene diversity) = 0.6253, H S (Within or sub population gene diversity) = 0.6225, D ST (Between or inter population gene diversity) = 0.0028 and G ST (Coefficient of Gene differentiation) = 0.0045) were calculated, and Nei’s standard genetic distance matrix was determined. The coefficient of gene differentiation (G ST ) represents that maximum genetic variation occurs due to variation within the population. Tharu of West Champaran represented the maximum distance from Rana Tharu (0.032), but most demes represent small distances (~<0.004). The dendrogram was constructed using the Unweighted Pair Group Methods with Arithmetic Mean (UPGMA) method to visualise the ethnogenetic relationship represented by bi-clustered population or clade-level diversification. Discussion The significance levels represent genetic stability of all blood groups. The complete absence of the A 2 blood group, very low prevalence of Rh negative and very high prevalence of the B group suggest racial similarities to Mongoloid population. The Bombay phenotype (O h ) is first reported from the Tharu population. The G ST of ABO indicates that only about 0.45% of the total genetic variation is due to differences between demes living in Indo-Nepal Terai, while 99.55% is present within the population. The genetic distance matrix indicates a strong shared ancestry and consistent gene flow within demes and a closely clustered population. The Danguria and Pachhimaha Tharus represent a common genetic stock, while Rana Tharu and Tharu of West Champaran are the ethnically most distinct groups.