Induction of Sex-linked Recessive Lethals and Visible Mutations by feeding X-irradiated DNA to Drosophila melanogaster

Abstract

ATTEMPTS to induce genetic changes by chemical means go back to early days of modern genetical research. Even when Muller's¹ discovery of the mutagenic effect of X-rays had opened up a new and exceedingly fruitful field of research, the search for chemical mutagens was not abandoned. In fact, during the last two or three decades, hundreds of chemicals have been tried for their mutagenic effect; however, most of these are highly toxic and are not found free in Nature. The search for a specific mutagen led Gershenson^2,3 to try calf-thymus nucleic acid for its mutagenic effect. Gershenson reared flies upon food to which a large amount of (5 per cent) thymonucleic acid was added and found that a considerable number of the imagos, derived from the larvae that had had this food, showed various characteristic abnormalities. When these flies were bred, similar abnormalities were often found among their progeny. A large number of wing-mutations were claimed to have been induced by this treatment and this led him to claim that mutations had been produced en masse. Gershenson, employing ClB-technique, could not find any increase in the induction of sex-linked-lethals (s.l.l). Rapoport⁴ repeated Gershenson's experiments and he too could not observe any increase in s.l.l. rate. Muller⁵ tried both thymonucleic and yeast nucleic acids and did observe some phenotypic abnormalities but again no increase in s.l.l. To quote Muller: “It is hardly conceivable that a variety of types of visible mutations could be induced en masse by any agent without there being some appreciable effect on the lethal mutation frequency also”. He was therefore of the opinion that there is no indication of either visible or lethal mutations induced by this treatment. On general considerations, one would not expect any harmful or mutagenic effect of the natural DNA, which forms an important part of the food consumed by every living organism. However, the possibility of such mutagenic effect of certain DNA's for certain organisms under given conditions could not be absolutely ruled out.