FERTILITY AND STERILITY IN DROSOPHILA 



163 



drawn off and tested in Fi generation. Much to my surprise, 

 all proved fertile. From 5 of these, seven pairs were made up in 

 the Fo, as shown in table 19. 



As a control of the white-eyed stock eight pairs were tested all 

 of which were fertile. 



Fifteen males, brothers of the sterile males whose fertility had 

 been established, were crossed with 15 white-eyed females; all 

 the pairs proved fruitful. Offspring from five of these crosses 

 were paired as shown in table 20. All the males represented in 

 the 62 pairs in the table have white eyes like the mother, while all 

 the females have red eyes like the father, since this is a case of 

 sex-linked inheritance. On inbreeding, four classes of offspring 

 will be produced in the next generation: (1) white-eyed males; (2) 

 red-eyed males; (3) white-eyed females; (4) red-eyed females. 

 The four classes were about equally represented. The virgin fe- 

 males were placed with a number of males; the males with a 

 number of virgin females. The result is given in table 21. 



TABLE 20 

 Sterility as it appeared among the children of the crosses; Fi generation 



TABLE 21 



Sterility as it appeared in the F^ generation. Offspring from two of the 21 pairs 



of No. 2, table 20 



Family No. 2 b 



