CHAPTER VII

MULTIPLE ALLELOMORPHS

The meaning of the term multiple allelomorphs
may be illustrated by the following example:

1.  If a white-eyed male of Drosophila is mated to
a red-eyed female, the F2 ratio of 3 reds to 1 white is
explained by Mendel's law, on the basis that the
factor for red is the allelomorph of the factor for
white.

2.  If an eosin-eyed male is mated to a red-eyed
female, the F2 ratio of 3 reds to 1 eosin is also ex-
plained if eosin and red are allelomorphs.

3.  If the same white-eyed male is bred to an eosin-
eyed female, the F2 ratio of 3 eosins to 1 white is
again explained by making eosin and white allelo-
morphs.

There are here three factors, any two of which
may meet, and whenever they do, they behave as
allelomorphs. They form a system of triple allelo-
morphs.

On the chromosome hypothesis the explanation of
this relation is apparent. A mutant factor is located
at a definite point in a particular chromosome; its
normal allelomorph is supposed to occupy a corre-
sponding position (locus) in the homologous chromo-
some.    If another mutation occurs at the same place,

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