28 



SEX-LINKED INHERITANCE IN DROSOPHILA. 



Because of the change that takes place as the culture grows older (the 

 abnormal changing to normal), this character is not of much value in 

 linkage work. The location of the factor in the X chromosome at 2.4 

 has been made outfrom the data given by Morgan (1915^). Thesedata, 

 which in general include only the abnormal classes, are summarized 

 in table i. 



Table 1. — Linkage data, from Morgan, 1915b. 



EOSIN. 



(Plate II, figures 7 and 8.) 



The recessive sex-linked mutation eosin eye-color appeared in 

 August 1911 in a culture of white-eyed flies (Morgan igi2a). The 

 eye-color is different in the male and female, the male being a light 

 pinkish yellow, while the female is a rather dark yellowish pink. Eosin 

 is allelomorphic to white and the white-eosin compound or heterozygote 

 has the color of the eosin male. There is probably no special sig- 

 nificance in this coincidence of color, since similar dilutions to various 

 degrees have been demonstrated for all the other eye-colors tested 

 (Morgan and Bridges, 1913). Since eosin is allelomorphic to white, 

 its locus is also at i.i. Eosin is the most useful character among 

 all those in the left end of the chromosome. 



BIFID. 



The sex-Hnked wing mutant bifid, which appeared in November 

 191 1, is characterized by the fusion of all the longitudinal veins into a 

 heavy stalk at the base of the wing. The wing stands out from the 

 body at a wide angle, so that the fusion is easily seen. At the tip 

 of the wing the third longitudinal vein spreads out into a delta which 

 reaches to the marginal vein. The fourth longitudinal vein reaches 

 the margin only rarely. There is very often opposite this vein a great 

 bay in the margin, or the whole wing is irregularly truncated. 



The stock of bifid was at first extremely varied in the amount of this 

 truncation. By selection a stock was secured which showed only very 

 greatly reduced wings like those shown in figures a, b. Another stock 

 (figs, c, d) was secured by outcrossing and selection which showed wings 

 of nearly normal size and shape, which always had the bifid stalk, 

 generally the spread positions (not as extreme), and often the delta and 

 the shortened fourth longitudinal vein. We believe that the extreme 

 reduction in size seen in the one stock was due to an added modifier of 



