A Mutant in Drosophila pseudoobscura Which Alters the Pigmentation of the Testicular Envelope without Changing that of the Eyes

Abstract

The mutant to be described in the present article has the property, unique among the known mutants in various species of Drosophila, in that it alters the pigmentation of the testicular envelope without at the same time affecting the coloration of the eyes of the fly. The more usual condition is that the pigment in the testicular envelope is absent or reduced in quantity in those mutants which show also a reduction of the amount of the red pigment in the compound eyes (see, for examples, the descriptions of the various mutants in Drosophila melanogaster in Bridges and Brehme, 1944). The mutant, to be called marbled (symbol mbl), was found in November, 1954 in a culture of D. pseudoobscura derived from a wild female collected at Bryce National Park, Utah, in the summer of 1951 by Professor Th. Dobzhansky. In the normal flies, the red coloration of the testis can easily be seen through the abdominal wall from the ventral side; in the marbled mutant the abdomen seems to be devoid of the color. Dissection of marbled males showed the condition to be due to a mosaic discoloration of the testicular envelope, which is mostly colorless except for irregular-shaped splotches of the normal red pigmentation. In the original culture only about 4 per cent of the males showed the marbled character. By back-crossing the daughters of marbled fathers to marbled males, 54 marbled and 110 normal males, together with 213 females, were obtained. Ten of the females were then crossed individually to marbled males. In three of the cultures all the sons were marbled, showing that the females as well as the males were pure for the gene mbl. A pure mbl stock was established from these cultures.