188 GENETICS 



The numbers in the squares indicate how many 

 times a brown determiner is present in each zygote. 

 It will be seen that only one out of the sixteen possi- 

 bilities lacks a brown-chaff factor, and this one will 



4 3 i t 



Number of doses of the brown determiner 



FIG. 54. The distribution of the sixteen possibilities resulting when two 

 similar determiners (brown-chaff) act together as a dihybrid. 



consequently produce only white chaff, while the re- 

 maining fifteen possibilities, each of which has at least 

 a single determiner for brown, will all yield brown 

 chaff. 



The brown-chaff factor, moreover, is present in 



