The difference is the purpose. The purpose of mutagenicity experiment is to verify the change of substance to biological heredity, and the purpose of genetic toxicology experiment is to verify the damage of substance to biological genetic material and its toxic effect on biology. To put it simply, mutation experiment studies causality, what causes what results, and genetic toxicology experiment studies process and what causes those results (genetic mutation of organisms is often toxic to organisms themselves, so the two experiments are often very close or the same in experimental process, results and recorded data).