41 8 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



The situation is thus explained by the dihybrid ratio, but although 

 only one character is involved that character depends upon two com- 

 plementary factors. 



Another situation is worth noting. No. 6 of the diagram is white 

 because it contains only one of the necessary factors; No. n is white 



FIG. 79. Diagram illustrating behavior of complementary factors in cross 

 between red-grained and white-grained corn. R and C must both be present to 

 produce red-grained corn. (From Coulter and Coulter.} 



for the same reason, but its germinal constitution is just the opposite. 

 What would happen if these two are crossed? There is only one 

 possibility, since each is a homozygote producing only one kind of 

 gamete. The result would be red, and thus a cross between two whites 

 would produce only reds. What would happen from crossing Nos. 6 

 and 15, the former being a homozygote and the latter a heterozygote ? 



