CHAPTER II
TYPES OF MENDELIAN HEREDITY

Experience has shown that Mendelian inheritance
applies to all sorts of characters, structural, physio-
logical, pathological, and psychological; to characters
peculiar to the egg, to the young, and even to old
age; to length of life; to fundamental taxonomic
characters as well as to "superficial" characters; and
to characters intimately concerned in maintaining
the life of the individual, as well as to characters which
apparently do not influence survival. Some of these
different types and their mode of inheritance will be
briefly described, but since the general principles in-
volved are more important than the kind of character
that is affected, the results will be treated under
general headings.

DOMINANCE   AND   ReCESSIVENESS

The four-o'clock (Mirabilis jalapa) has a white and
a red-flowered variety. If these are crossed the hy-
brid is pink in color. The pink hybrid inbred (self-
fertilized in this case) gives in the next generation
(F2) one red, to two pink, to one white (Fig. 14).
Owing to the intermediate color of the hybrid (or
heterozygote) it is impossible to say that either
color dominates the other.    The factor for red and

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