346 



GENES MODIFYING NOTCH. 



Half of the daughters are normal, half are heterozygous Notch. 

 The normal daughters and normal sons never transmit the Notch 

 gene, which, therefore, never gets into the male hne or into the line of 

 normal daughters. 



Fig. 91. 



Dexter obtained his mutant in a cross between beaded and wild. 

 The Notch that I used arose independently in descendants of ves- 

 tigial flies, in which stock the factor may have already existed. This 

 mutant has, however, originated several times in other cultures in the 

 laboratory. It is by no means one of the rarer mutations. 



VARIATION OF NOTCH. 



The most conspicuous character of the female heterozygous for 

 Notch is the serration at the end of the wings (fig. 91) caused by the 

 absence of the marginal bristles and generally accompanied by a slight 



