GENES MODIFYING NOTCH. 300 



FOURTH TEST (FOR FOURTH-CHROMOSOME MODIFIERS). 



The following method of findrng out whether a niodifyinfr j^cne it^ 

 present m a particular chromosome was su^^ested by Dr. .\. 11. Sturte- 

 vant. A short-Notch female is first crossed to a hhirk pink hcnt nuile. 

 The Fi males^ are then crossed (in pairs) to stock short-Notdi females 

 (see scheme below). 



Sladk. pinl^ I-x-tH 6 



W Slioil Kotcli ( 



F„ Notch p 



b>' Short Notch O 



biy Black piukb«-nt O 



Since the Fi male had one fourth chromosome from black pink bent 

 (and since there is no crossing -over in the male), half of his Notch (Fj) 

 daughters will have this chromosome (only one each), and half will not 

 have it. If they are of two sorts (so classified in table 12), such as 

 intermediate and short Notch, their differences might depend on the 

 presence of the bent fourth chromosome in half of the Notch females. 

 If now we separate as far as possible the females into two classes, and 



Table 12. — Fi cf {out of short Notch 9 by hmt cf ) by short Notch 9 . 



test each female separately to find out if she has or hiis not a l)ent 

 fourth chromosome, we should get an answer to our question. Each 

 female was bred to a black pink bent stock male. The presence of 

 black, of pink, and of bent (separate or combined) in the offspring wiis 

 recorded. Table 13 gives the end-results; the first column records the 

 kind of F2 female tested, the next three columns the kind of notch, and 

 the next three columns indicate (by X) whether l)lack. pink, or l>ent 

 was present; and the last column the total number of fliei>. 



* Their sisters that were not recorded here wore nil atavi.stic Notch. 



