GENES MODIFYING NOTCH. 



363 



The results of such a test are given in table 7. The table includes 

 only females and only the red-eyed females (the flies that are genet- 

 ically Notch), while the eosin ruby females and all of the males were 

 thrown away. Examination of the table shows that practically all 

 of the not-Star, not-Dichsete females have normal wings (potentially 



TABLE 7. 



Notch). 1 This is the class that contains the original second and third 

 chromosomes and their modifying genes if such were present. Con- 

 versely, practically all of the Star-Dichsete females are atavistic, and 

 this class contains the Notch females that have received the second 

 and the third chromosomes from the Star-Dichsete males. Thus far 

 the evidence shows that the change that took place during selection is 

 caused by something in one or the other or both of these two chromo- 

 somes. Whether both or only one is shown by further analysis of the 

 results. For instance, the fact that all the Dichsete flies are atavistic, 

 and the fact that all not Dichsete are selected type, shows that the 

 modifier is in the third chromosome. Had the modifying gene or 

 genes been in the second chromosome, then all Star-eyed females 

 should be atavistic, which they are not, and, conversely, all not- Star- 

 eyed females should be selected type, which they are not. Hence 

 the modifier in question is not in the second chromosome. 



Finally, the same evidence proves that the modifiers that caused 

 the change are not in the sex chromosome as recessive modifiers be- 



1 In this table (also in tables 4 and 5) the + sign indicates that the number of flies that 

 follow were notched in only one wing. 



