It can hardly be due to imitation for the trait is
such a slight one that most people have not noticed it before their
attention is called to it by the geneticist. Furthermore, babies are
found almost always to clasp the hands in the same way every time. The
trait is a good illustration of the almost incredible minuteness with
which heredity enters into a man's make-up. Photograph by John Howard
Paine.]
The sweet pea offers a good illustration of the widespread effects which
may result from the change of a single factor. In addition to the
ordinary climbing vine, there is a dwarf variety, and the difference
between the two seems to be proved, by exhaustive experimental breeding,
to be due to only one inherited factor. Yet the action of this one
factor not only changes the height of the plant, but also results in
changes in color of foliage, length of internodes, size and arrangement
of flowers, time of opening of flowers, fertility and viability.
Again, a mutant stock in the fruit fly (Drosophila) has as its most
marked characteristic very short wings. "But the factor for rudimentary
wings also produces other effects as well. The females are almost
completely sterile, while the males are fertile.
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