Micronucleus formation in preimplanted mouse embryos cultured in vitro after irradiation with x-rays and neutrons.

Preimplanted mouse embryos cultured in vitro were irradiated with X-rays and neutrons in the late G2-phase of the 2-cell stage. Both radiation qualities induced micronuclei at very low doses. The kinetics of micronucleus formation during the first and second cell cycles after X-irradiation depended on the radiation dose and on the extent of the division delay. New micronuclei appeared to be formed even after the third and later post-irradiation mitoses. The shape of the various dose-effect curves and the mechanism of micronucleus formation by the two radiation qualities are discussed.