The influence of high and low temperatures on the expression of tumorous head in Drosophila melanogaster.

N a previous paper (GARDNER and WOOLF 1949) a character expressed as I abnormal growths in the head of Drosophila melanogaster was discussed. The expression was shown to be dependent upon two genes, one sex-linked and one autosomal. The sex-linked gene ( tu-f) was shown to control a maternal effect expressed only in the presence of the third chromosome semidominant gene tu-3). The penetrance in the inbred stock (symbolized tu-h) homozygous for tu-l and tu-3, was 76 percent a t 22'C. Outcrosses involving females from the tu-h stock and males from laboratory stocks produced an average of about 30 percent of abnormal flies in the F1 a t 22'C. Reciprocal outcrosses between tu-h males and females from laboratory stocks other than Oregon produced less than 1 percent of abnormal flies in the F1. Oregon females were shown to behave like tu-h females in producing the maternal effect. Small percentages, not exceeding five percent of abnormal flies were obtained in the Fz from both reciprocal crosses involving all except one of the laboratory stocks studied. Higher percentages were obtained fromscrosses involving a stock containing aristaless, dumpy, dachs, black, curved, plexus and speck on one second chromosome and Curly and speck on the other second chromosome (a1 d p d b c p x sp /Cy sp) suggesting the presence of a modifier in this stock. The objective of the present paper is to report the results of experiments designed to determine the effect of different temperatures upon the expression of the character. Preliminary investigations indicated that the penetrance and expressivity increase proportionally with temperatures from 15'C to 30'C. The viability was shown to be considerably decreased a t 30°C, the females showing a greater inviability than the males a t temperatures above 22'C. The preliminary results also indicated a temperature effective period a t an early stage in development. The flies were raised in half-pint milk bottles on the standard cornmeal, agar, molasses media.