Sibship asymmetries of rhesus blood groups in the presence of maternal antibodies.

The genotypes of the children of R1r, R2r, and R1R2 fathers, and Rh-immunized rr mothers, were examined. R1r fathers had an excess of R1r over rr children, and R1R2 fathers had an excess of R1 r over R2r children. These asymmetries confirm the findings of a previous study. The possibilities of artefactual self-selection, of genotyping errors, and of errors in assigning paternity, were examined and excluded. Alternative models of genetic transmission and of antigenic structure were studied, but no basis for explaining the findings was found or formulated. Three possible biological explanations were formulated including (a) asymmetric segregation of the rhesus genes, (b) selective early fetal loss, and (c) a selective effect upon the performance of sperms bearing different haplotypes. The first of these three appeared unlikely. The data did not provide a basis for supporting or rejecting or differentiating the other two.