BLENDING INHERITANCE 



187 



miners for the character of red color, each of which 

 is able to give red color to the wheat. Taken together, 

 these three determiners behave cumulatively, follow- 

 ing the law of a trihybrid. 



For example, if a brown-chaffed wheat with the for- 

 mula BB\ in which B and B' each represent a brown- 

 chaffed factor, is crossed w^ith a white-chaffed wheat of 

 the formula bb\ in which b and b' each represent the 

 absence of B 

 and B^ respec- 

 tively, then all 

 the progeny of 

 this cross will be 

 brown-chaffed, 

 having the zy- 

 gotic formula 

 BBW. When 

 upon matura- 

 tion the gametes 

 form out of the 

 germ-cells from 

 such hybrids, 

 the following 

 four combina- 

 tions are pos- 

 sible, and no 

 others : BB\ Bb\ bB\ bb\ These represent, there- 

 fore, the possible gametes present in each sex of the 

 first filial generation, and upon intercrossing they can 

 combine into sixteen possible zygotes to form the 

 second filial generation, as shown in Figure 53. 



Fig. 53. — Diagram of the possible combinations 

 in the F2 generation of brown-chaffed wheat 

 according to experiments of Nilsson-Ehle. B 

 and B' are cumulative factors for the brown- 

 chaff character, b and b' denote the absence of 

 B and B' respectively. 



