Why is the XX Fitter? Evidence Consistent with an Effect of X-heterosis in Women from Sex Ratio Data in Offspring of First Cousin Marriages

@article{Hook1973WhyIT,
  title={Why is the XX Fitter? Evidence Consistent with an Effect of X-heterosis in Women from Sex Ratio Data in Offspring of First Cousin Marriages},
  author={Ernest B. Hook and William Jack Schull},
  journal={Nature},
  year={1973},
  volume={244},
  pages={43-46}
}
ALTHOUGH women are known to be more viable than men, the biological mechanisms for this difference are poorly understood. A relevant question is, to what extent does heterozygosity for X-linked loci contribute to survival of the XX female? The advantage accruing to the XX female through having this factor can be defined as X-heterosis1. Practically all serious X-linked disorders such as haemophilia occur in males, but the total incidence of such severe diseases is relatively small and cannot… CONTINUE READING