No. 644] MUTANT CHARACTERS IN DROSOPHILA 



235 



descriptive section. But the evidence for their being 

 parallels is made particularly strong by the fact that 

 their genes are completely or almost completely linked 

 in both species. In melanogaster yellow and scute are 

 located at the extreme end (zero point) of the chromo- 

 some map, while in mlUstonl they are approximately 

 in the middle. 



A situation similar to- this has already been found in 

 D. ohscura (according to unpublished data of D. E. 

 Lancefield). Here the characters yellow and scute also 

 bear a close resemblance to those in melanogaster and 

 are verj' closely linked. As in wilUstoni, the factors for 

 yellow and scute are near the middle of the chromosome 

 map. It will be recalled that ohscura, like irillisfojii, has 

 a large V-shaped X-chromosome — although the other 

 chromosomes are different (Metz, 1916). In the two 

 species having V-shaped X-chromosomes, then, yellow 

 and scute are ''located" near the middle of the chromo- 

 some map, while in melanogaster with its short, rod-like 

 X-ehromosome, yellow and scute are at one end. As Lance- 

 field has pointed out in his discussion of ohscura, this sug- 

 gests that one end of the rod-like X in the one case cor- 

 responds to the middle of the V-shaped X in the other. 

 And this suggests that the rod-like chromosome itself 

 may correspond to one arm of the \ . 



The onlv evidence in irillisfoui on the latter hypothesis 

 is that furnished by the cluiraeter^ forked and stnl>hy. 

 These are possible ])arallels of the singed and forked in 

 melanogaster. They are similar in a general way in the 

 two species (see description above), and the serial order 

 of the genes is the same (Fig. 18), altliougli the linkage 

 relations do not agree exactly. 



In this connection it may be recalled that "yellow," 

 "singed" and "forked" have also l)oen found in Droso- 

 pJiiln ririlis (Metz. 1*»lf^. and unimblished data), and 

 may, likewise, he r-on^idered a- |>ossible parallels to those 

 in nn'hntnr/nsf, r. J'Irilis ha> a rod-like X-cliromosome 

 reseml>ling that of nielanogasf'-r, and the relative posi- 



