MENDEL’S LAWS OF HEREDITY 389 
(segregates) the two chromosomes carrying the character for tallness, 
so that each gamete contains one. This occurs for the other characters 
as well as for that of tallness. From the tall plant, therefore, all the 
gametes will contain the character for tallness, and from a dwarf plant 
all of the gametes would contain the character for dwarfness. When 
these two individuals are crossed the zygote will contain both charac- 
ters, and these two characters will be transmitted together in the 
succeeding cell generations. The individual from such a zygote of 
course would be tall, but at the same time it would be carrying a 
recessive determiner for dwarfness, and this fact would be shown by 
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Fic. 68.—Diagram illustrating behavior of first hybrid generation (F,) when 
inbred. Illustrates meaning of ‘“‘segregation”’ and “‘purity of gametes’’ and how 
chance matings of F; gametes result in 3:1 ratio in F; generation; dwarf indi- 
vidual produced only by zygote in lower right-hand corner. (From Coulter and 
Coulter.) 
its behavior in breeding. The result of inbreeding such hybrids is 
indicated in the accompanying diagram (Fig. 68), which represents 
the chance matings of two kinds of gametes. The obvious results are 
three tall individuals and one dwarf. This is the so-called monohybrid 
ratio, which means the ratio when a single pair of allelomorphs is 
considered. 
Before discussing the further development of Mendel’s law it will 
be necessary to explain some of the terminology of genetics. When 
each gamete carries the same kind of determiner the zygote is said to 
receive a double dose; when a zygote receives only a single such deter- 
miner it is said to receive a single dose. In Fig. 68 one zygote receives 
a double dose of tallness and two others a single dose. These phrases 
are more or less common in the literature of the subject, but the more 
