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The Effect of Oxygen Concentration upon the Induction by X-Rays of Melanotic Tumors in Drosophila melanogaster

( Department of Biology, The Johns Hopkins University, Baltimore, Md.)

1. Studies of a particular stock of Drosophila melanogaster have shown that it contains a suppressor gene that inhibits the manifestation of erupt, a mutant that produces an abnormal growth of hypodermal tissue which erupts through the center of the eye. The action of the suppressor-erupt gene is blocked when the embryos are x-rayed.

2. The same stock possesses an unprecedented tendency to produce melanotic tumors when the embryos are x-rayed.

3. Both the incidence of tumors and the incidence of erupt increase significantly and linearly for increasing O₂ concentrations at the time of irradiation, over the range from 0 to 20 per cent. Although there is only a small further increase as the shift is made from air to pure oxygen, this increase is also significant for both effects.

4. In addition, both the mortality and duration of development also increase with increasing oxygen concentration at the time of x-ray treatment.

5. The same differential responses to x-rays in varying concentrations of oxygen also occur in another tested stock, Oregon-R, which is not closely related to the suppressor-erupt stock; but in the case of the Oregon-R stock all responses show a much lower incidence. Thus, it seems possible that the system affected is a general one, at least for Drosophila melanogaster.

6. The incidence of melanotic tumors in both stocks is slightly, but significantly, increased by exposure of the embryos for 10 minutes to pure O₂, without x-ray treatment. It is decreased by similar exposure to pure N₂. In this respect the tumor response differs from the response of suppressor-erupt, which is not affected by oxygen alone, in the absence of x-ray treatment.

Received 6/27/52.

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