Segregation distortions for the ABO system in pairs of sibs.

The influence of maternal phenotype was observed in 471 consecutive sib pairs to explore the segregation distortions for the ABO system. The ABO typing was done using the standard technique of haemagglutination reaction and the sib pairs were named according to their phenotypes. Thus A-B is the pair where first sib was A and the consecutive one was B. The statistical computations involved calculations of ABO gene frequencies, and application of chi-square and Z test for proportions to study the segregation distortions in sibs. A significant excess of B gene in the first sib and reduction of O in the second sib was observed when the Z test was applied to study the covariance, whereas no significant distortions were observed with simple Chi-square test. Heterozygote AO mothers segregated insignificantly in favour of A allele whereas BO mothers segregated significantly in favour of B allele in the first as well as in the second sib indicating that selection is favouring the B gene in our population.