A comparison of mutagenic effects by 2 MeV neutrons and 200 kVp X-rays in prophase I oocytes of the silkworm, Bombyx mori L

This paper reports the results of experiments on the relative biological effectiveness (RBE) of 2 MeV neutrons as compared with 200 kVp X-rays for recessive visible mutation induction on prophase I oocytes in the silkworm. Eleven-day-old pupae or 2--3 days before emergence were treated with five different doses (450, 900, 1800, 3600 and 5400 rads) of 200 kVp X-rays and three different doses (500, 1000 and 2000 rads) of 2 MeV neutrons. Mutations at the pe and re loci were detected by the egg-color specific locus method. The dose-response relation for X-rays was deviated slightly from the linear relation, but that for 2 MeV neutrons was linear so that the RBE value varied according to the mutation frequency compared: at 0.5% level the RBE was about 3.0 and at 1.5% it was reduced to 1.8. The frequency of whole-body mutations was higher at the re locus than at the pe locus regardless of radiations, but the case was reversed for the fractional-body mutations. The ratio of frequency of fractional-body mutations to whole-body mutations was 0.1 at the two loci. Possible explanations for the above findings were discussed. (auth.)