14 



Scientific Phoceedings. 



io (619) 



A dominant sex-limited character. 

 By T. H. MORGAN. 



[From the Department of Zoology, Columbia University.] 



A new mutant of the fruit fly, Drosophila, characterized by 

 abnormal arrangement of the black bands on the abdomen, 

 proves to be dominant to the normal arrangement of the bands, 

 and since the factor for the character is coupled with femaleness 

 it may be assumed to be contained in the X-chromosome. Abnor- 

 mal 9 by normal cT gives abnormal males and females. These 

 inbred produce in the next, or F 2 , generation 50 per cent, abnormal 

 9, 25 per cent, abnormal cf and 25 per cent, normal cT. No 

 normal females appear in this generation. Thus the normal 

 character is sex-limited in relation to the abnormal. 



The reciprocal cross, viz., normal 9 by abnormal d 1 gives 

 abnormal females and normal males. These inbred produce in 

 the next, or F 2 , generation, 25 per cent, abnormal 9 , 25 per cent, 

 normal 9. 25 per cent, normal d\ and 25 per cent, abnormal 

 c? 1 . The explanation is as follows : 



Abnormal 9 = Ab. X - Ab. X. 



Normal d" = N. X . 



Fi 9 Ab. X N. X. 



& Ab. X 



Ft Ab. X Ab. X = Ab. 9 . 



Ab. X N. X = Ab. 9 . 

 Ab. X = Ab. d". 



N. X = N. cT. 



It will be seen that the abnormal factor is contained in X, 

 hence sex-limited inheritance. The explanation of the recip- 

 rocal cross will be clear from this example. 



Five other cases of sex-limited inheritance have been found 

 in Drosophila, Viz., miniature wings, rudimentary wings, black 

 color, bright red eye and orange eye. All of these are recessive 

 characters, and ex hypothesi are also present or absent from X. 

 By crossing a red-eyed, abnormal type with a white-eyed, normal 



1 Since the abnormal character overlaps the normal some difficulty is found in 

 classifying the Fs generation. 



