GENES MODIFYING NOTCH. 



367 



It will be noticed in table 10 that in addition to the short Notch 

 there are others called intermediate and even atavistic. That these 

 are for the most part due to fluctuations of the short-Notch character 

 itself is almost certain, since even in stocks bred for 20 generations 

 for short Notch a similar range occurs in some bottles, but when tested 

 the "atavistic" (or more generally the "intermediate" Notch) give 

 the same kinds of daughters as do their sisters, the short Notch females. 



TABLE 10. 



SECOND TEST. 



In this test the reciprocal cross was first made, viz, Star Dichaete 

 female by eosin male of short-Notch stock. The FI male gets his X 

 chromosome from his Star Dichaete mother. Consequently if it is 

 the X chromosome in the short-Notch stock that carries a recessive 

 modifier for Notch (that has both the Notch-bearing X and its normal 

 homologous chromosome) no short-Notch daughters are expected when 

 the above Ft male is mated to a short-Notch stock female. 



The result of mating such FI Star Dichaete males to short-Notch 

 females is shown in table 11. Practically all of the Notch females are 

 atavistic or slight Notch. The result is in striking contrast to the 

 result in the first test and means, obviously, that the X chromosome 

 contains one or more modifiers that shortens the effects of the Notch 

 factor itself. That some of the Notch females are atavistic and some 

 slight may be expected, since separation of the two classes is difficult 

 or impossible and no emphasis can be laid on the classification as it 

 stands. 



