190 GENETICS 



numbers at the two extremes. In this instance 

 six out of sixteen individuals of the second gen- 

 eration theoretically present a perfect "blend" be- 

 tween the original brown- and white-chaffed grand- 

 parents, although complete segregation has actually 

 occurred. 



The same explanation holds true as displayed in 

 Figure 55 for the trihybrid case of red- and 

 white-kerneled wheats in which only one white- 

 kerneled to sixty-three red-kerneled individuals ap- 

 pear in the second filial generation. The number 

 of red determiners in each zygote is indicated by the 

 figure at the bottom of each square. The large screw- 

 head symbols with vertical, horizontal and diagonal 

 slots each represent an independent determiner for 

 red kernel, while the small screw heads symbolize 

 the absence of each of these determiners, or white 

 kernel. When the pure strain of red-kerneled wheat 

 is crossed with a pure strain of white-kerneled wheat, 

 the first generation is all a heterozygous red of a 



Pure red -h cuhite = Hybrid red 



Fig. 56. — The result of crossing white wheat with trihybrid red wheat. 



somewhat lighter shade than the original pure red 

 strain. 



When plants of this heterozygous sort are crossed 

 together, they yield plants producing red-kerneled 

 and white-kerneled wheats in the proportion of sixty- 

 three to one. The sixty-three kinds of red wheats are 



