[Illustration: WHITE BLAZE IN THE HAIR
FIG. 19.--The white lock of hair here shown is hereditary and
has been traced back definitely through six generations; family
tradition derives it from a son of Harry "Hot-Spur" Percy, born in 1403,
and fallaciously assigns its origin to "prenatal influence" or "maternal
impression." This young woman inherited the blaze from her father, who
had it from his mother, who had it from her father, who migrated from
England to America nearly a century ago. The trait appears to be a
simple dominant, following Mendel's Law; that is, when a person with one
of these locks who is a child of one normal and one affected parent
marries a normal individual, half of the children show the lock and half
do not. Photograph from Newton Miller.]
[Illustration: A FAMILY OF SPOTTED NEGROES
FIG. 20.--The piebald factor sometimes shows itself as nothing
more than a blaze in the hair (see preceding figure); but it may take a
much more extreme form, as illustrated by the above photograph from Q.
I. Simpson and W. E. Castle. Mrs. S. A., a spotted mutant, founded a
family which now comprises, in several generations, 17 spotted and 16
normal offspring. The white spotting factor behaves as a Mendelian
dominant, and the expectation would be equal numbers of normal and
affected children.
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