FERTILITY AND STERILITY IN DROSOPHILA 



143 



It seemed probable that the defect was due to something in the 

 hereditary mechanism rather than to some factor in the environ- 

 ment, since the same defect reappeared among the grandchildren 

 which hatched at different times during a period of two months. 

 Since the effects of inbreeding were under observation I was at 

 first inclined to attribute this sterility to inbreeding. 



STERILITY AND INBREEDING 



It is a popular belief that one of the effects of inbreeding is to 

 induce sterility. Moenkhaus and Castle, however, after many 

 generations of inbreeding with Drosophila could find no evidence 

 in favor of such a view. Nevertheless, since sterility appeared in 

 my 'inbred' culture to such a high degree it was tempting to 

 attribute it to inbreeding. As Moenkhaus has clearly pointed 

 out, if in a sterile inbred stock, the sterility can be eliminated 

 by continued inbreeding, then inbreeding can not be held to be 

 the causative agent. This is the test to which my own case has 

 been put, and by selecting from those families that showed the 

 sterility in the least degree a fertile race was produced. Tables 

 1 to 7 show the manner in which the sterility appeared in the 

 inbred stock and its elimination by selection. 



TABLE 1 



Sterility of the first five inbred 

 generations 



Sterility of the inbred stock 



TABLE 2 



Sterility in the Fe generation 



GENERATION 



NO. 



I PAIRS 

 1 TESTED 



PAIRS 



STERILE 



Fi 



F2 



F, 



F,* 



Total. 



16 

 16 

 7 

 12 

 10 



61 



1? 







3 



3 



2 



STERILE STERILE 

 9 Cf 



The ten pairs of Fs were from a sin- 

 gle pair of F4 



* Miscellaneous paira. 



