at the 1-cell (or “zygotic”) stage [1–4]. In the Heiligenberger strain, radiation exposure during the preimplantation period with doses higher than 0.5 Gy also revealed to be able to induce a genomic instability, expressed by an increase of chromosomal aberrations in the fetuses. This radiation effect was already present in normal fetuses but was more pronounced in the malformed ones, suggesting a link between genomic instability and the malformation [8,9].
However, studies with C57BL mice revealed that the genomic instability was also present in this mouse strain after zygote irradiation, and that the effect was even higher than in the Heiligenberger strain. Consequently, this effect appeared to be of a more general nature [8,9].