e 



324 MUTATIONS IN EYE-COLOR OF DROSOPHILA. 



One of the first mutants that appeared had white eyes, i. e., eyes without 

 any color except in so far as white may be called a color. In fact the white e\ 

 is not a transparent eye but is distinctly white. This effect might be due to 

 interference of light waves, as in white snow flakes, or it might be due to white 

 pigment. It is difficult to state positively which of these views is correct for the 

 white eye, but a white pigment is present, and I am inclined to attribute the 

 whiteness, in part, to this condition. 



The white eye is due to the loss of a color producer C. Since white-eyed flies 

 may belong to any one of the eye colors given above, i. e. , by suitable combina- 

 tions it may be shown that there are white-eyed flies that carry the determiners 

 for vermilion, others for pink. The discovery of a new mutant lacking orange has 

 shown, however, that when the factor C is lost the factor for orange is also lost. 

 These two factors appear closely linked, and generally go together. The evidence 

 for this interpretation will be given later. The white-eyed series is represented 

 by the following formulae : 



(Red) White 9 VPocXVPocX] 



(Red) White <? VPocXVpoc 



(Vermilion) White 9 VpocXVpocX 

 (Vermilion) White cf VpocXVpoc 

 (Pink) White 9 vPocXvPocX 



(Pink) White tf 1 vPocXvpoc 



(Orange) White 9 vpocXvpocX 

 (Orange) White d 1 vpocXvpoc 



Before taking up the experiments dealing with the new mutant that lacks 

 orange, I wish first to consider certain cases that were not clear from the earlier 

 studies. Their reexamination has furnished striking proof of the correctness 

 of the interpretation that was there followed. 



Fig. 6. 



The Red-Pink Ratio. 



In the crosses between red-eyed and pink-eyed flies reported in my former 

 paper, the Pinks ran far behind their schedules in the F 2 generation. The 

 expectation both for females and males is three Reds to one Pink. The actual 

 F 2 ratio in one cross was 20 to 1 ; and in the reciprocal cross the F 2 ratio was 5 to 1. 

 The striking difference between the realized and the expected ratios could 

 only be attributed to the viability of the pink flies. In order to test this combi- 

 nation once more I asked one of my students, Mr. Joseph Liff, to repeat the 

 experiment; and at the same time to make back crosses, and counter crosses; 

 as well as to take counts of individual pairs of the flies. His results are as follows : 



Red 9 420 



j? n u d „ R 9 I Red tf 413 

 R 9 by P <? 



#c? 



Pink 9 104 

 I Pink <? 94 





