Homoeotic effect of the tumorous-head mutant and differential effect of an enhancer gene in the tumorous-head strain of Drosophila melanogaster.

Homoeotic effects (one organ replaced by an organ from a different part of the body) were investigated in the tumorous-head phenotype in Drosophila melanogaster. The tumorous-head mutant is the only known maternally effected homoeotic mutant (Postlethwait and Schneiderman, 1973). As reported by Postlethwait et al. (1972) transformations from eye to abdominal like structures, eye to antennal like structures, eye to palpus like structures, rostralhaut to genital like structures, rostralhaut to clasper teeth, and rostralhaut to antennal like structures were observed. Transformations currently observed but not by Postlethwait et al. (1972) are: eye to genital structures (resembling anal plates in both sexes or lateral plates in males); antenna to genital like structures; rostralhaut to abdominal like structures; and proboscis to leg like structures. Since a tumorous-head strain selected for high penetrance and expressivity was used for this study, differences between the two studies are ascribed to strain selection. Effect of a third chromosome gene which acts to enhance the tumorous-head maternal effect was also investigated. A highly significant increase in expressivity was found especially in females. Of 4,730 female flies examined possessing the enhancer gene, high penetrance and high expressivity, only the eye-antennal imaginal disc and possibly the libial disc showed destabilization. We observed no destabilization of the wing disc by the tumorous-head genes as predicted by Kauffman (1973).