No. 575] 



AX APTEROUS DROSOl'II 1 LA 



677 



apterous fly become Op-a P , and those for the winged fly 

 A P -A P . In other words, A P is a factor in the wild fly 

 necessary for wing production, while a P is its modified 

 homologue responsible for lack of wings in the mutant. 

 The apparent contradiction in using A v , not for the factor 

 responsible for apterous, but for its normal allelomorph, 

 may be confusing at first sight, but a little familiarity with 

 the system obviates this difficulty. 



Experiment I.— Long-winged, red-eyed J 1 by apterous, 

 white-eyed $ (from miniature wing stock). 



F x All winged. Long-winged, red-eyed females. 



Miniature winged, white-eyed males. 



F 2 Winged and apterous as follows : 



i Long- winged, red-eyed males and females. 

 Long- winged, white-eyed males and females. 

 Miniature-winged, red-eved males and 

 females. 

 Miniature-winged, white-eyed males and 

 females. 



. f Apterous, red-eyed males and females. 



Apterous I Apterous, white-eyed males and females. 



This experiment shows the inheritance of the apterous 

 character to be Mendelian, giving in F, all winged, and in 

 F 2 approximately 3 winged to 1 apterous. Table I con- 

 tains a summary of the offspring from 21 pairs of the F, 

 and F 2 individuals, giving a total of 1,405 winged to 450 

 apterous,— a ratio of 3.12 to 1. 



The absence of apterous flies in F t indicates at once 

 that the apterous character is not sex-linked. The pres- 

 ence of miniature-winged flies in F 1 and F 2 indicates that 

 the apterous factor is independent of the miniature-wing 

 factor, which latter must have been carried by the apterous 

 female (coming from miniature wing stock), and trans- 

 mitted to her offspring unaffected by the apterous factor. 



