Parenthood and heredity / Sheldon C. Reed.

  • Reed, Sheldon C. (Sheldon Clark), 1910-2003.
Date:
1964
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Parenthood and heredity / Sheldon C. Reed. Source: Wellcome Collection.

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    Clubfoot 127 embryo upon the expression of the character should be empha¬ sized. A paper by Book (1948) considered the evidence for a genetic background for congenital clubfoot and quite correctly started by reviewing the research on twins. His Table I, on the expression of clubfoot in the two kinds of twins, is reproduced here as Table XVIII. The identical twins show both members with clubfoot 10 times as frequently as the fraternal twins. Fur¬ thermore, Book showed that the frequency of clubfoot among the sibs of single-birth children affected with clubfoot is 3 per cent, exactly the same figure as that for a second affected twin of the two-egg type. This means that having two embryos in the same uterus does not in itself increase the frequency of ex¬ pression of clubfoot. It also shows that the gene or genes for club¬ foot, when present, are expressed in only about one-third of the embryos (32 per cent) having these genes. Consequently, the internal environment of the embryo is very important in deter¬ mining whether or not the genes for clubfoot will be expressed. A study of the frequency of children with clubfoot among the progeny of first cousin marriages was enhghtening. Book found that 27 per cent of the sibs of the clubfoot propositi also had clubfoot in the families where the parents were first cousins. When the parents were not blood relatives, the usual 3 per cent of clubfoot among the sibs of the propositi was observed. This provides a clue to some of the variation in expression of the character. When blood relatives produce children, one expects that some of the recessive genes that were hidden in the com- Table XVIII The Occurrence of Clubfoot in the Two Kinds of Twins Both Members with Clubfoot One Member with Clubfoot Identical Fraternal 13 (32%) 4 (3%) 27 130