Sex ratio in spina bifida and anencephaly

Timson's (1969, 1970) three locus model for the determination of anencephaly and spina bifida is examined, and it is concluded that observed population incidences of these conditions do not fit the model. A consideration is presented of the relevance of such models to the aetiology of multifactorial disease.     

The sex ratio in spina bifida

It is shown that the well known excess of females in spina bifida children is statistically significant when they are compared with (a) the general population and (b) their sibs.Although there is a small excess of males amongst the sibs this is not statistically significant when compared with the general population and when all the children in these families are considered they appear to have a sex ratio very similar to that general population. The sibs of the parents of spina bifida children show a statistically significant excess of females.These findings are discussed with particular reference to the genetics of spina bifida.