Genetic effect of chronic exposure of male mice to gamma-rays

The frequency of reciprocal translocations (RT) in mouse spermatogonia induced by gamma-rays at doses of 1.5-4.5 Gy and dose rates of 2.7 X 10(-6), 5.8 X 10(-6), 9.4 X 10(-5) and 4.5 Gy/min was studied. At all dose rates there was a linear increase in the RT frequency with increasing dose. At a dose rate of 9.4 X 10(-5) Gy/min, the RT frequency was on average 10 times lower than that for a single acute dose rate of 4.5 Gy/min. Further dose rate reduction did not result in a decrease in the RT yield, and at the lowest dose rate of 2.7 X 10(-6) Gy/min and a dose of 3.0 Gy the RT frequency was higher than at dose rates of 5.8 X 10(-6) and 9.4 X 10(-5) Gy/min and the same dose. Possible reasons for an increase in the RT frequency at low dose rates are considered. A study of the frequency of occurrence of abnormal sperm heads (ASH) has shown that a dose rate of 9.4 X 10(-5) Gy/min, this frequency is independent of an accumulated dose and is the same as that at an acute dose of 3.0 Gy. At dose rates of 2.7 X 10(-6) and 5.8 X 10(-6) Gy/min, ASH frequencies were only slightly increased at all doses compared to the control level.