However, experiments with ionizing radiation, the simplest mutagen to study, indicate that the developing brain is particularly ill prepared to deal with mutagenic insults and is consistently affected. Hence, microcephaly is the only consistent finding in non-lethal mutagen exposures during pregnancy, but is clearly not an effect exclusive to mutagen exposures. As with any developmental toxin, increasing the dosage of experimental mutagen exposure during pregnancy also leads to miscarriage. Mutagens can also affect germ cells and there is general concern about environmental exposures leading to birth defects through mutations in egg or sperm cells. Experimental studies, however, show that significant exposures to mutagens are not likely to be detected by increased rates of birth defects.
Germ cells are more likely to be killed by DNA damage than to be mutated.
This loss of cells will lead to infertility. Mutations in germ cells could introduce new genetic conditions into families, but only those conditions that are dominant and whose phenotypes are viable will be seen. Experimental data indicate that most dominant mutations induced in germ cells at high levels of exposure are lethal. Conceptions carrying dominant lethal genes are likely to abort early or even fail to implant. Thus the perceived effect is, again, infertility.