Preliminary study on chromosomal aberrations in eggs of mice fertilized in vitro after X-irradiation

The X-ray induction of chromosomal aberrations in the eggs of mice fertilized in vitro was studied by using a fertilization technique developed by Yamada et al. (1982a,b). Mature sperm, eggs just before insemination and zygotes at the early pronuclear stage were irradiated with 40 R of X-rays. In a control and two groups of irradiated sperm or unfertilized eggs, most of the 1-cell eggs progressed to the metaphase stage (92.2-94.4%) at 15-17 h after insemination. In the group irradiated at the early pronuclear stage, 38.2% of the 1-cell eggs were still at the pronuclear stage; furthermore, a delay of chromatin condensation in one of the pronuclei was often observed. The frequency of chromosomal aberrations in the irradiated zygotes (20.6%) was much higher than that in the irradiated sperm (2.9%) or in unfertilized eggs (11.0%).