Tests of the effects of γ-radiation on eye color mutation frequencies in Dahlbominus have shown no indication of differences in repair when chronic exposures were compared with acute at three different exposure levels (62.5, 250, and 500 R). Also, an almost exact linear relationship between dose and effect was found when tests with acute exposures (100 R/min) were extended to cover the range from 500 down to 15.5 R, indicating that a threshold value at lower levels is improbable. The adult females irradiated in these tests were held until 9-13 days of age, when all germ cells were arrested in the mature oocyte stage, thereby eliminating varying sensitivity to mutation during prolonged chronic exposures. The sensitivity of Dahlbominus oocytes has proved to be approximately five times higher than that found in mice. The doubling dose for Dahlbominus, where the induced frequency is twice the spontaneous frequency, appears to be approximately 24 R.

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