For a variety of organisms, the probability of a spontaneous gene mutation is of the order of 10−5 to 10−6 per gene per generation, and is substantially independent of the life span. Experiments on several types of organisms have shown that irradiation can produce gene mutations. These induced mutations are not novel types, but appear to be entirely similar to those which occur spontaneously. When the irradiation is carried out at a rate of 0·6 roentgens per hour, or higher, the average probability of inducing a gene mutation is about 3 × 10−8 per gene per röntgen. The spontaneous mutation rate is, therefore, very much higher than could be expected as a result of the cosmic radiation and local γ radiation (0·3 mr/day) and is, therefore, due to other causes than irradiation. When the irradiation of experimental organisms is carried out at a low rate (order of 1 to 8 röntgens per day) no induced mutations have yet been reported in the organisms studied (fruit fly, mouse). This suggests that the effective average radiation sensitivity of immature sperm and eggs may be less than the sensitivity of mature sperm and eggs. Dominant mutations may become visible in the first generation offspring. Recessive mutations may appear only in homozygous individuals of a later generation, and, therefore, recessive mutations accumulate in the population as a result of both spontaneous and induced mutations. From the appropriate mathematical theory, and the experimental data now available, it seems safe enough to conclude that no detectable increase in hereditary abnormalities is likely to result, even after many generations, if a small fraction of the population receives daily radiation doses up to 0·1 röntgen per day.
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Robley D. Evans (1950) studied this question.