230 



THE SECOND-CHROMOSOME GROUP 



MORULA (m,). 



(Plate 10, figures 3a and 36.) 



ORIGIN OF MORULA. 



In the F2 from the cross of peach (third-chromosome recessive, 

 allelomorph of pink) by wild, two red males were found that had only- 

 very inconspicuous bristles on the thorax (M 20, March 8, 1913). 



INHERITANCE OF MORULA. 



These two males were out-crossed to wild females, and in Fi pro- 

 duced only wild-type males and females. Four Fi mass-cultures were 

 made up, and in F2 these produced (table 77) a total of 1,950 flies, of 

 which 432 or 22.2 per cent were ''spineless." The ''spineless" flies 

 were exactly as numerous among the F2 females as males, from which 

 it follows that the character is an autosomal recessive mutant. There 

 was found to be some little difficulty in classification, and it is certain 

 that a few of the genetically spineless individuals were included among 

 the wild-type; this was especially true in culture M 42. 



Table 77. — Pi, '^ spineless'* {morula) d^cT X wild 9 9; Fi wild-type cf cf 



and 9 9 inbred en masse. 



FEMALE STERILITY OF MORULA. 



The next step attempted was to secure a pure stock of "spineless" 

 by mating together en masse several of the F2 individuals from M 31. 



It was discovered that this stock culture was not showing any larvae, 

 so the flies were put in a fresh bottle and several other "spineless" 

 males and females added. This culture also failed. The F2 cultures 

 had been thrown away meanwhile, so that it was not possible to start 

 other stock cultures. The flies were then taken from the mass-culture 

 that had failed, separated as to sexes, and the males out-crossed to 

 wild females and the females to wild males. 



The out-cross of the males was successful, but the female out-cross 

 failed entirely. The trouble, then, was confined to the females, which 

 so far as tested (about 15 females) had been entirely sterile both with 

 similar males and with wild males. 



The "spineless" females that hatched in the F2 from the male out- 

 cross were tested very extensively. Probably as many as 150 such 



