Studies of Eye Pigments of Drosophila

HE red and brown eye pigments of Drosophila melanogaster are different T in their properties and developmental history. The formation of the brown pigment depends on diffusible substances derived from tryptophane; that of the red pigment apparently does not. Hence, a t least the final stages of the reaction chains leading to the formation of these pigments follow different paths. However, some mutant genes inhibit to various degrees the development of both pigments, and this suggests the existence of a common step in the two sequences of reactions. The nature of this common step is unknown. I ts understanding would further clarify the mechanism of pigment formation and of its genetic control. One might expect that a study of the two pigments in a mutant whose phenotype is affected by environmental conditions would throw some light on their relationship. The mutant blood (wbz-a member of the series of multiple alleles a t the white locus) shows such a dependence on temperature. I ts eye color is pale brownish yellow a t 3ooC, and deep reddish purple a t 17OC, with intermediates a t temperatures between these two extremes. The primary purpose of the work reported here was to (I) determine the period of maximum sensitivity to temperature for each of the pigment components, and ( 2 ) describe in quantitative terms their variation with temperature. In the course of the investigation the question arose as to whether the changes with temperature are purely quantitative, and this has led us to (3) examine the absorption spectra of the pigments contained in the eyes of flies raised a t different temperatures.