ORIGIN AND DESCRIPTION OF BRISTLE IN 

 DROSOPHILA MELANOG ASTER. 



ROBERT L. KING, 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF PENNSYLVANIA. 



ORIGIN AND DESCRIPTION OF BRISTLE IN D. melanog aster. 



In an experiment designed to test the combined effect of tem- 

 perature and the genes linked with Curly upon crossing-over in 

 the third linkage group, Dichsete females were mated with sepia 

 spineless sooty rough Curly males. Among the 163 offspring of 

 such a mating there appeared on April n, 1925, two Dich?ete 

 females with the bristles on the head and thorax shorter (1/2 to 

 3/4 the length of corresponding bristles on the wild type) and 

 slightly thicker than those in the wild type and slightly irregular 

 in outline with a tendency to be twisted and truncate. The new 

 character is called Bristle in. the following account (Symbol Bl.). 

 The fact that only two unusual females were found among so many 

 made it seem improbable that the character difference depended 

 upon a recessive or a sex-linked factor difference. Thus by ex- 

 clusion, it was supposed that the mutant gene was dominant. 

 Further the two individuals probably owed their appearance to a 

 single mutation which may have occurred either in the late 

 oogonial divisions of the female, or, in the spermatocyte or late 

 spermatogonial divisions of the male parent. Since the male 

 carried the dominant Curly and the female the dominant Dichsete 

 it is more probable that the mutation occurred in the female since 

 both individuals were not Curly. 



These two females were mated with wild type males and their 

 offspring (which were not counted) included Dichsete, Bristle, 

 Dichaete Bristle and wild type flies. A number of the female 

 Dichcete Bristle offspring were mated separately with homozygous 

 Lobe males. Half the offspring were Bristle which supported the 

 assumption that Bristle was dominant; half the Bristle individuals 



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