FERTILITY AND STERILITY IN DROSOPHILA 165 



On mating the Fi the following results : 



wX - Rx ^ 



-^ ^ Gametes 

 w A. — (J 



wwXX— wRXx— wXO — RxO F2 White-eyed females, red-eyed 

 females, white-eyed males, red-eyed males; no sterile individuals. 



This does not accord with the sterility as shown in this 

 experiment. 



c. If the defect is brought in the X-chromosome of both grand- 

 parents, it follows: 



w X — w X ^ 



Ti r\ dametes 



R X — O 



wRxx — wRXx — wxO — wXO Fi Red-eyed females, white-eyed 

 males. Half of the females sterile. 



On mating the Fi the following results: 



w X — R X „ 



^ Gametes 

 w X — O 



wwXx — wRxx — wXO — RxO F2 White-eyed females and red-eyed 

 females; white-eyed males and red-eyed males; red-eyed females sterile. 



This accords with the appearance of the eye colors but not with 

 the appearance of the sterility, since there was practically none 

 inFi. 



These three assumptions exhaust the possibilities on the 

 hypothesis that the defect is carried by the X-chromosome and 

 yet none of them meets the facts in the case of this experiment. 

 I conclude, therefore, that sterility as it affected the female in this 

 experiment was not transmitted by the X-chromosome. There 

 is a possibility, however, that the factor involved is in the sex 

 chromosome but so far from W that it crosses over freely with it. 



DISCUSSION 



The foregoing series of experiments brings out the foUpwing 

 facts. (1) Sterility as it appeared in the inbred stock affected 

 primarily the females. The males may also be sterile but it seems 

 probable that the sterility of the male bears no causal relation to 

 the sterility that affects the female. (2) The defect is genninal 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 17, NO. 1 



