Apparent Interaction Between the Xg^a Blood Group System and the Sex Ratio: A Note of Explanation

Abstract

PROF. J. H. Bennett has called to our attention a possible source of confusion in our recent letter¹. We left implicit the assumption that the expected sex-ratios in the two classes, ‘Before and including the first female’, and ‘After the first female’, were equal, and we failed to make clear that the numbers of children in our Table 1 included those from all-male sibships. If such sibships had been omitted, the sex ratio (male: female) would indeed have been expected to be higher in the first class than in the second, but when they are included, as was done, the expected ratios are equal. Other explanations of our observation, such as selective family limitation, do not account for its limitation to the single Xg—Xg^a mating type where the postulated ‘incompatibility’ could occur.