Human Reproduction vol.11 no.5 pp.939-94O, 1996 OPINION Genetic and non-genetic determinants of the human sex ratio at birth

I should like to raise two main points in connection with the recent note by Bernstein (1995). Firstly, the possible genetic control of human sex ratio and secondly, the variances of the distributions of the combinations of the sexes in human sibships and in litters of polytocous mammals. Possible genetic control of human sex ratio Bernstein's suggestion that there is some genetic control of sex ratio is supported by the evidence that some parental HLA genes may partially control offspring sex ratios. Ivanyi et al (1972) reported that in the mouse 'a genetic factor identical with, or closely linked to, the H-2 system is involved in the control of sex hormone metabolism'. On the basis of this, they made a remarkable prediction: 'If the situation in histocompatibility genetics and associated traits in man is analogous with that seen in the mouse, a great numbe