Some Developmental Effects of X-Rays in Drosophila

If Drosophila larvae homozygous for the third chromosome recessive straw-3 are treated with X-rays, back-mutations of the straw-3, gene to its normal allelomorphs take place in somatic cells, and the cells of the wings give rise to hairs which can be recognized as wild type (Waddington, 1940b). In one attempt to follow out this matter in more detail high doses (7000 r. units) were applied. The resulting mortality was, it might be said, 100 %. That is, no flies emerged; but on dissecting the pupa cases, it was found that a considerable proportion had developed up to the hatching stage, but had not been able to free themselves from the pupal integuments. These flies were found to exhibit some rather remarkable deformities, and the experiment has therefore been repeated a number of times. It is the purpose of the present paper to describe in some detail the developmental abnormalities produced by such heavy doses of X-rays. Friesen (1936) originally described some abnormalities (which he termed ‘Roentgenmorphoses’) produced by slightly smaller doses, and some further notes on such cases have been published by Enzmann & Haskins (1938a, b) and Haskins & Enzmann (1937). All the abnormalities found by these authors can probably be considered as due to inhibitory actions of X-rays on various developmental processes; but, as will be clear later, the striking feature of the animals to be discussed in the present communication is that in some of them the growth of certain rudiments has been actually stimulated by the radiation. A preliminary communication of the experiments recorded in this paper has been published (Waddington, 1942).