528 



THE AMERICAN NATURALIST 



[Vol. LI 



There is a mutant called ''notch" (Fig. 1) character- 

 ized by a serration at the ends of the wings. The factor 

 that causes this is sex-linked, dominant in regard to the 



wing character but recessive in its letlial effect. A female 

 with notch wings carries the gene in one of her X-chromo- 

 -omes and the normal allelomorx>h in the other X-chromo- 

 -oHie. Half of her sons get the former and die, the other 

 half get the latter X-chromosome and live. As there are 

 no ictlin! l)t'aTing males, the ffMiiah's iim<t in fvery gen- 

 .'i ati<.ii hi' hrcd to iioi-iiial i!iah->. Kor twenty uonerations 



come together in the same female one X-chi-omosome 

 carrying the gene for notch and its mate carrying the 

 normal allelomorph. Selection of those females that 



