DILUTION EFFECTS AND BICOLORISM IN CERTAIN 

 EYE COLORS OF DROSOPHILA 



T. H. MORGAN AND C. B. BRIDGES 



The Zoological Laboratory, Columbia University 



As shown in a colored plate in an earlier paper/ there is strik- 

 ing bicolorisna in the eye color called eosin. In pure cultures the 

 eye color of the female is a yellowish pink while that of the male 

 is a pinkish yellow, more translucent, and less intense. It was 

 shown further, that when an eosin female is crossed to a white 

 male, the sons are of the ordinary color for eosin males, but the 

 daughters instead of being red or even dark eosin, are of the 

 same color as the sons. The sons are eosin, because eosin is a 

 sex-linked character, that is, the factor which differentiates be- 

 tween eosin and red is carried by the sex chromosome, unpaired 

 in the male of Drosophila. The one sex chromosome which the 

 son has, came directly from his mother, both of whose sex chro- 

 mosomes bore the factor for eosin. 



The explanation at that time offered was that the dark eye 

 color of the mother was due to the fact that she was duplex with 

 regard to the 'color producer' (i.e., the allelomorph dominant to 

 white) while the light color of the son was explained as the result 

 of his being haploid for that same factor. It was assumed that 

 the white eyed flies lacked the color producer,' consequently the 

 daughters from the cross of colored females by white males should 

 be haploid with regard to the color producer. Their composi- 

 tion should then be the same as that of the brothers, that is, both 

 should show the color of the eosin male. But if we assume that 



1 Further experiments with mutations in eye-color of Drosophila. Jour. Acad. 

 Nat. Sciences, Philadelphia, vol. 15, Second Series, November, 1912. 



429 



