Chromosomal damage in preimplantation mouse embryos and its development through the cell cycle.

Cytogenetic damage is usually studied in the first metaphase after exposure to ionizing radiation although it is well known that further chromosomal aberrations are also expressed during later mitotic divisions (Bauchinger et al., 1986; Lloyd et al., 1992). For such investigations the preimplantation mouse embryo is very well suited. If irradiation takes place in the 1-cell stage it can easily be followed whether the cells of the embryo have reached the first, second or third mitosis after the exposure. Furthermore, the duration of the various cell cycle phases is well known and therefore radiation effects on the cell cycle, e.g., the G2 block, can be investigated (Streffer and Molls, 1987). Studies on these two phenomena will be reported here.