48 



SEX-LINKED INHERITANCE IN DROSOPHILA. 



Table 23. — Pi bow 9 X arc d^. 



In this case the F2 expectation is 6 straight to 10 not-straight. Since 

 the sex-Hnked gen bow entered from the female, half the F2 males 

 and females are bow. The half that are not-bow consist of 3 straight to 

 I arc, so that both in the female classes and in the male classes there 

 are 3 straight to 5 not-straight or in all 6 straight to 10 not-straight. 

 The realized result, 248 straight to 307 not-straight, is more nearly a 

 3 : 4 ratio, due probably to a wrong classification of some of the bow as 

 straight. 



LEMON BODY-COLOR. 



(Plate I, figure 3.) 



A few males of a new mutant with a lemon-colored body and wings 

 appeared in August 1912. The lemon flies (Plate II, fig. 3) resemble 

 quite closely the yellow flies (Plate II, fig. 4). They are paler and the 

 bristles, instead of being brown, are black. These flies are so weak 

 that despite most careful attention they get stuck to the food, so that 

 they die before mating. The stock was at first maintained in mass 

 from those cultures that gave the greatest percentage of lemon flies. 

 In a few cases lemon males mated with their gray sisters left off'spring, 

 but the stock obtained in this way had still to be maintained by breeding 

 heterozygotes, as stated above. But from the gray sisters heterozygous 

 for lemon (bred to lemon males) some lemon females were also produced. 



LINKAGE OF CHERRY, LEMON, AND VERMILION. 



In order to study the linkage of lemon, the following experiment was 

 carried out. Since it was impracticable to breed directly from the 

 lemon flies, virgin females were taken from stock throwing lemon, and 

 were mated singly to cherry vermilion males. Only a few of the females 

 showed themselves heterozygous for lemon by producing lemon as well 

 as gray sons. Half the daughters of such a pair are expected to be 

 heterozygous for lemon and also for cherry and vermilion, which went 

 in from the father. These daughters were mated singly to cherry 

 vermilion males, and those that gave some lemon sons were continued. 



