NEW DATA. 



47 



The F2 ratio in table 21 is evidently the 2:1:1 ratio typical of sex- 

 linkage, but with the bow males running behind expectation. This 

 deficiency is due in part to viability but more to a failure to recognize 

 all the bow-winged individuals, so that some of them were classified 

 among the not-bow or straight wings. In favor of the view that the 

 classification was not strict is the fact that the sum of the two male 

 classes about equals the number of the females. 



BOW BY ARC. 



When this mutant first appeared its similarity to arc led us to suspect 

 that it might be arc itself or an allelomorph of arc. It was bred, there- 

 fore, to arc. The bow male by arc females gave straight (normal) 

 winged males and females. The appearance of straight wings shows 

 that bow is not arc nor allelomorphic to arc. When made later, the 

 reciprocal cross of bow female by arc male gave in Fi straight-winged 

 females but bow males. This result is in accordance with the inter- 

 pretation that bow is a sex-linked recessive. Further details of these 

 last two experiments may now be given. The Fi (wild-type) flies from 

 bow male by arc female were inbred. The data are given in table 22. 



Table 22. — Pi bow d^ X arc 9 - 



Bow and arc are so much aUke that they give a single rather variable 

 phenotypic class in F2. Therefore the F2 generation is made up of only 

 two separable classes — flies with straight wings and flies with not- 

 straight wings. The ratio of the two should be theoretically 9 : 7, 

 which is approximately realized in 179: 133. 



If the distribution of the characters according to sex is ignored, the 

 case is similar to the case of the two white races of sweet peas, which 

 bred together gave wild-type or purple peas in Fi and in F2 gave 9 

 colored to 7 white. If sex is taken into account, the theoretical expec- 

 tation for the F2 females is 6 straight to 2 arc, and for the F2 males 3 

 straight to i arc to 3 bow to i bow-arc. 



The Fi from bow females by arc male and their Fo offspring are given 

 in table 23. 



