Further evidence for maternal effect and modifiers of tumorous head genes in natural populations of Drosophila melanogaster.

An inherited abnormality (Figs. 1-9), consisting of irregular growths of various sizes in the head region of the tuk strain of Drosophila, is under investigation. The strain was obtained from Dr. Wilson Stone and appeared in 1945 in a culture of flies obtained at Acahuizotla, Mexico, in 1941 by a collecting party from the University of Texas. Two interacting genes, tu-1 in the first chromosome and tu-3 in the third chromosome, are responsible for the trait (8). Since tu-1 or its alÃ-eleshas been found in several natural populations, it is possible that this gene was already present in the Mexico collection and that only tu-3 arose by mutation. The descriptive term "tumorous head,"1 sym bolized tuh, has been used to identify the trait and the flies which carry the genes. The description of the abnormality (4, 8,13), genetic mechanism (8), influence of temperature on expression (9), and relative viability (5) of tumorous head flies have been presented. A maternal effect controlled by tu-1 was interpreted from the results of reciprocal outcrosses (8). Both wild and mutant stocks from the labora tory were tested for alÃ-elesand modifiers of susceptibility genes. Three of 21 wild stocks (6) carried alÃ-eles of tu-1. Modifiers increasing the per-