"
[Illustration: THE EFFECT OF ORTHODACTYLY
FIG. 17.--At the left is a hand with the third, fourth and
fifth fingers affected. The middle joints of these fingers are stiff and
cannot be bent. At the right the same hand is shown, closed. A normal
hand in the middle serves to illustrate by contrast the nature of the
abnormality, which appears in every generation of several large
families. It is also called symphalangism, and is evidently related to
the better-known abnormality of brachydactyly. Photograph from Frederick
N. Duncan.]
[Illustration: A FAMILY WITH ORTHODACTYLY
FIG. 18.--Squares denote males and circles females, as is usual
in the charts compiled by eugenists; black circles or squares denote
affected individuals. A1 had all fingers affected in the way shown in
Fig. 17; B2 had all but one finger affected; C2 had all but one finger
affected; D2 had all fingers affected; D3 has all but forefingers
affected. The family here shown is a branch, found by F. N. Duncan, of a
very large family first described by Harvey Cushing, in which this
abnormality has run for at least seven generations. It is an excellent
example of an inherited defect due to a single Mendelian factor.]
One of the best attested single characters in human heredity is
brachydactyly, "short-fingerness," which results in a reduction in the
length of the fingers by the dropping out of one joint.
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