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 
(F.) 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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