FURTHER EXPERIMENTS WITH MUTATIONS IN EYE-COLOR OF 



DROSOPHILA: THE LOSS OF THE ORANGE FACTOR. 



Thomas Hunt Morgan, Ph.D. 



In previous papers (1910-1911) dealing with the inheritance of eye color in 

 mutants of the fruit fly Drosophila ampelophila, I have shown that the red color 

 of the eye of the wild fly is due to the presence of at least four factors. These 

 factors are vermilion (F), 1 pink (P), and orange (0), and a color producer (C). 

 The red eye has all four factors present, and may be represented by the formula 

 VPOC. The vermilion eye has V and present, but has lost the pink factor. 

 It is designated by VpOC. The pink eye has V absent, and is therefore vPOC. 

 The orange eye contains neither V nor P, and is therefore vpOC. Of these 

 factors P and C have been found to be sex-linked ; that is, they follow the factor 

 that in duplex produces the female sex, and, since the factor for femaleness goes 

 with the sex-chromosome, the factors P and C may be said to he in this chro- 

 mosome. When present they are represented in duplex in the female and 

 simplex in the male. The full formulae therefore for the eye-colors, and the 

 sex-factor are as follows : 



Red eye 9 VPOCXVPOCX LT>1 x VVX7TTT n , 



J> A , Trr^TTxr h Plate XXVIII, fig. 1 



Red eye d" VPOCXVpoc J ' & 



Vermilion eye 9 VpOCXVpOCX LT31 A VVTrTTT n n 



, r ... ir n/>vir ^Plate XXVIII, fig. 2 



Vermilion eye cf VpOCXVpoc J 



Pink eye 9 vPOCXvPOCX YYVT __ 



w»u „ , nr\mr (-Plate XXVIII, fig. 3 



Pink eye & vPOCXvpoc J ' 6 



Orange eye 9 vpOCXvpOCX YYV ttt <u a. 



n™«~ , r\nv kPlate XXVIII, fig. 4 



Orange eye d" vpOCXvpoc J 



In my former papers the distribution of the orange factor could not be given, 

 because the factor had never been lost. Whether, for instance, it is sex-finked, 

 in the sense that the factor P is sex-linked, or whether it is present in all the 

 eggs and sperm, as is the factor V when present, was not apparent; for, the 

 the results would be the same so long as all of the eggs and the female pro- 

 ducing sperm contain the factor for orange. 



But later a mutant appeared that had lost the factor for orange, as suitable 

 matings made clear. It was then discovered that the factor, 0, is also sex-linked ; 

 and m the complete formulae, given above, the factor is omitted from all the 

 male-producing sperm. Its absence is indicated by small 0. 



1 In my former papers the factor was designated by R. 



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