218 GENETICS 



above a black symbol represents the grossulariata 

 factor linked with a sex chromosome. The variety 

 lacticolor occurs whenever the factor for grossulariata 

 is absent. In this case two sex determiners are neces- 

 sary to produce a male, and only one to produce a 

 female. In the following theoretical diagrams the 

 actual number of offspring obtained by Doncaster 

 and Raynor in each cross is indicated outside the circles 

 that represent the zygotes, and the parenthetical 

 numbers refer to the five kinds of individuals cata- 

 logued in Figure 67. 



In the first cross (Fig. 68) where a lacticolor female 

 (5) and a grossulariata male (1) were bred together, 

 the entire progeny was grossulariata in character with 

 an approximate equality between the sexes, that is, 

 45 males (2) to 50 females (4). 



When these hybrid grossulariata individuals, (2) and 

 (4), were mated with each other in Cross 2 (Fig. 69), 

 the character of grossulariata appeared again in both 

 sexes, (1), (2), and (4), while the character lacticolor 

 was confined as usual to females alone (5). It was 

 only when grossulariata hybrid males (2) were crossed 

 back to lacticolor recessive females (5) in Cross 

 3 (Fig. 70) that individuals of both varieties and 

 both sexes appeared, (2), (3), (5), (4), in practically 

 the expected equal numbers, namely, 63, 65, 70, 62. 

 The lacticolor male (3) obtained by bringing together 

 the two sex determiners necessary for maleness, each 

 of which had been dissociated through the foregoing 

 crosses from the sex-limited grossulariata factor, was en- 

 tirely new to science, never having been found in nature. 



