74 



SEX-LINKED INHERITANCE IN DROSOPHILA. 



necessary for such a special study. In the case of green we might 

 perhaps have employed a similar method, performing all experiments 

 with a common difference from the gray in all flies used. 



CHROME. 

 In a stock of forked fused there appeared, September 15, 191 3, 

 three males of a brownish-yellow body-color. They were uniform in 

 color, without any of the abdominal banding so striking in other body- 

 colors. Even the tip of the abdomen lacked the heavy pigmentation 

 which is a marked secondary sexual character of the male. About 20 

 or more of these males appeared in the same culture. This appearance 

 of many males showing a mutant character and the non-appearance 

 of corresponding females is usual for sex-linked characters. In such 

 cases females appear in the next generation, as they did in this case 

 when the chrome males were mated to their sisters in mass cultures. 

 Since both females and males of chrome were on hand, it should have 

 been an easy matter to continue the stock, but many matings failed, 

 and it was necessary to resort to breeding in heterozygous form. The 

 chrome, however, gradually disappeared from the stock. Such a 

 difficult sex-linked mutation as this could be successfully handled 

 (like a lethal) if it could be mated to a double recessive whose members 

 lie one on each side of the mutant, but in the case of chrome this was 

 not attempted soon enough to save the stock. 



LETHAL 3. 

 In the repetition of a cross between a white miniature male and a 

 vermilion pink male (December 1913), the F2 ratios among the males 

 were seen to be very much distorted because of the partial absence of 

 certain classes (Morgan 1914c)- While it was suspected that the 

 disturbance was due to a lethal, the data were useless tor determining 

 the position of such a lethal, from the fact that more than one mother 

 had been used in each culture. From an F2 culture that gave practi- 

 cally 3 2:1 sex-ratio, vermilion females were bred to club males. 

 Several such females gave sex-ratios. Their daughters were again 

 mated to vermilion males. Half of these daughters gave high female 

 sex-ratios and showed the linkage relations given in table 55. 



Table 55. — Linkage data on club, lethal 3, and vermilion, from Morgan, ipi/fc. 



