BLOOD GROUPS AND FERTILITY IN A JAPANESE POPULATION, WITH SPECIAL REFERENCE TO INTRAUTERINE SELECTION DUE TO MATERNAL‐FOETAL INCOMPATIBILITY

Abstract

Summary: In order to study whether there is differential fertility between different mating types of ABO, MN and Q systems, an investigation has been carried out on the population samples of two mining town areas, Ashibetsu and Kohnomae in Hokkaido. The material comprises 741 couples in Ashibetsu and 688 couples in Kohnomae. As the areas were found to be homogeneous in regard to the distributions of each blood group as well as of mating types, further analysis was made using the pooled data. It has been revealed that there is no indication of any selective force with respect to MN and Q mating types, while in the classical blood groups there are differences in human fertility between certain mating types.In the present data two different selective forces have been found in ABO mating types. The first one, arising from maternal‐foetal incompatibility, has been observed in the differential fertility between compatible and incompatible mating groups. The frequencies both of abortions per pregnancy and childless couples in the incompatible matings are, essentially higher than those in the compatible ones. A highly significant reduction in the mean number of living children has been observed in the incompatible matings compared with that in the compatible matings. This selection is operating to reduce the gene ratios of A and B and to increase the gene ratio of O. Mortality rate of the children of heterozygous genotypes incompatible with the mother has been roughly calculated as 21 % in this population.The other selective force has been observed in the differential fertility within certain compatible mating types. The mean numbers of pregnancies as well as of living children in A x A matings were significantly higher than those in A♀×O♂ and in AB♀×O♂ matings. It has been further revealed that, if compatible matings are divided into two subgroups, the matings in which the father belongs to O group have significantly lower fertility than those matings in which neither parent belongs to O. The effect of this second selection upon gene ratios is in the opposite direction to that of the first one, so that the losses of A and B genes eliminated through incompatibility could be compensated in the population.