Counseling in medical genetics / Sheldon C. Reed.

  • Reed, Sheldon C. (Sheldon Clark), 1910-2003.
Date:
[1955]
Catalogue details

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

Credit: Counseling in medical genetics / Sheldon C. Reed. Source: Wellcome Collection.

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    CLUBFOOT vironment of the embryo upon the expression of the character should be emphasized. A paper by Book (1948) considers the evidence for a genetic background for congenital clubfoot and quite correctly starts by reviewing the twin research. His Table I, on the expression of clubfoot in the two kinds of twins, is reproduced here as Table XIII. The identical twins show both members with clubfoot ten times as frequently as the fraternal twins. Furthermore, Book shows 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 expression of clubfoot. It also shows that the gene or genes for clubfoot, when present, are expressed in only about one-third of the embryos (32 per cent) having these genes. Conse¬ quently, the internal environment of the embryo is very important in determining whether or not the genes for clubfoot will be expressed. A study of the frequency of children with club- TABLE XIII THE OCCURRENCE OF CLUBFOOT IN THE TWO KINDS OF TWINS. 66