Genealogical study of human twinning.

Abstract

The inheritance of human twinning was studied by investigating: twinning among the children of twins and their sibs; the repeat twinning rates. The data were obtained from the archives of the Genealogical Society of the Church of Jesus Christ of Latter Day Saints at Salt Lake City, Utah. The major hypothesis tested was that dizygotic twinning is determined by one or more recessive genes, expression of which is limited to the female. The results of this study supported the hypothesis. The twinning rates among children of female dizygous twins and their female sibs were significantly higher than those for male dizygous twins and their male sibs. Under the single gene hypothesis of maternal recessiveness, an estimate was made of q, the frequency of the twinning gene. The value obtained for q was in the range from 0.33 to 0.52, the estimate of q2 therefore being from 0.11 to 0.27. The results led to rejection of the single gene hyopthesis of maternal dominance. The level of rates indicates that if twinning is controlled by a single gene, the rate of penetrance is low.