Abstract
The effects of oxygen and nitrogen post-treatments on X-ray-induced dominant lethality were studied in Stage 7 oocytes of Drosophila melanogaster. Irradiations were carried out under anoxia, in air or in an oxygen atmosphere. A wide range of exposures from 1000 R to 14000 R was used, the actual range depending on the gaseous atmosphere in which the flies were irradiated. The results indicate that ( 1) the dose-response survival curves obtained with either post-treatment are predominantly two-target and ( 2) with oxygen post-treatment the egg-survival is consistently higher relative to that observed with nitrogen post-treatment. The latter observation is interpreted as indicating oxygen-mediated repair of radiation-induced dominant lethal damage in State 7 oocytes. From the available data the oxygen-enhancement-ratio (O.E.R.) for dominant lethal induction in this germ cell stage is estimated to be about 2.6.
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