Induction of in vivo somatic mutations by low dose radiation in mice -threshold and dose rate effects-.

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Genetic effects of low dose radiation were examined with the use of in vivo somatic mutation method (PH-HTF1)in mice.Dose rate effects were also tested with the same method.1.Induction of in vivo somatic mutations with 10R of X rays:PT female was mated with HT males, and then 10R of X rays(55-62R/min)was given on the 10-1/2 the day of gestation.F1 mice (a/a,b/+,pc^<ch>/++,d/+,pa/+,pe/+,in/+)were sacrificed 6 weeks after birth,and colored spots were examined on the non-agouti(black)background.30 spots were found in 746F1 offspring(0.04)after 10R exposure,whereas 22spots were found in 750 unexposed controls. There is no significant diviation from linear dose response relationship between 0 and 130 R.2.Induction of in vivo somatic mutations by chronic exposure:110 R of X rays were given at different dose rate,55-62R/min,1 R/min,0.5R/min in the same time schedule.32.5R was also given at 0.1R/min.Numbers of mutants per F1 were 26/218(0.119),23/116(0.198),25/161 (0.155),and 8/59(0.136),respectively.3.Numbers of survived target cells and mutation rate per locus per R:Numbers of target cells were estimated from the ratio of total numbers of hair and mutant hairs.Estimated numbers of target cells were 530,1211,1853,and 3500,respectively.Consequently,mutation rate per locus per R was 1.9x10^<-7>,1.6x10^<-7>,0.8x10^<-m>,and 1.1x10^<-7>at dose rate of 55-62 R/min 1.0R/min,0.5R/min,and 0.1R/min,respectively,The results were compatible with those by specific locus mutations for spermatogonia.Threshold/Dose rate effect/Human genetic risk