422 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
Fig. 80 illustrates the situation and shows why all the individuals of 
the F, generation are white. It is interesting to note further the 
possibilities of white and red in the F, generation, They would be 
RR) ®@I|@ CiCze 
White 
Fic. 81.—Diagram showing some possible combinations in F; when F, of 
Figure 80 is inbred. Individual on left end of upper set red-grained, because R 
and C both present and J absent; other individuals in upper set white, because 
lacking C or R or both; individuals in lower set with inhibitory factor and there- 
fore white, whatever other combinations of factors they may contain. (From 
Coulter and Coulter.) 
numerous, since we are dealing with trihybrid ratios (see Fig. 81). 
This does not exhaust the possibilities, for the cases given were 
homozygotes, each producing a single kind of 
(R) (*) gamete. There remains for consideration the 
heterozygote situation (see Fig. 82). 
(c) (<) The possible mechanism of the inhibitory 
factor is as follows. We have assumed that red is 
G) ae produced only when the enzyme is present to 
oxidize the chromogen. Enzymes are very sensi- 
Fre, 82. From tive; their activities may be affected or com- 
Coulter and Coulter.) Pletely checked by various agents. Suppose that 
I of the diagram be such an agent and the neces- 
sary mechanism is apparent. When J is present R is paralyzed, so 
that it cannot oxidize C. 
3. Supplementary factors.—A supplementary factor is one that is 
added to a dissimilar factor, with the result that a character is modified 
in some way. 
