GENES MODIFYING NOTCH. 



383 



Truncate is a mutant that frequently appears in our cultures. It 

 has also appeared in the selection experiments. The ends of the 

 wings are cut off squarely. As it is dominant, especially in certain 

 stocks, it is likely that it would much effect the character of the Notch 

 when it occurred with it. Truncate appeared several times in the 

 course of the experiment. 

 The character of the trun- 

 cate Notch flies is shown in 

 figure 103, a, b, c, d. 



Beaded has appeared sev- 

 eral times in the course of the 

 work (fig. 104), and while no 

 tests have been made to 

 establish its relation to stock 

 beaded, it is not unlikely that 

 it is sometimes the same. 

 Since beaded often affects the 

 ends of the wings, and since 

 Notch itself often has a de- 

 fective outer margin to the 

 wing, the similarity of the 

 two stocks is in some flies very 

 striking. But the common 

 beaded is not sex-linked. 



A stock which, when 

 crossed to vestigal, produces flies many of which have a Notch on the 

 end of the wings has been isolated by Dr. C. B. Bridges. It has no 

 relation to Notch and appears in both sexes. (See "Nick, " page 273, 

 Part II.) 



On several occasions males (also females) have been ftfund in which 

 a little piece is cut out from the end of one or from both wings, (fig. 

 105 a, b, c). Superficially one gets the impression that the Notch 

 character has appeared in a male. These males have been bred, and 

 have never transmitted the character, so that there can be no doubt 

 that the variation has nothing whatever to do with Notch and is 

 possibly only a somatic defect, or more probably is a multiple-factor 

 character. The only way, in fact, that Notch might appear in a male 

 would be through somatic segregation in a female embryo of such a 

 kind that the Notch-bearing chromosome became dislocated and car- 

 ried to the anlage of the wing, leaving the other chromosome to produce 

 a male. Such a result has not been observed and it would be difficult 

 to establish the case if it really occurred. The sex-linked mutant 

 " serrate" that was present in the Star Dichsete stock is also a good 

 mimic of Notch. 



FIG. 102. 



