External Agents in the Induction of Gene and Chromosome Alterations
All strains have genetic constitutions that make them more susceptible to penetration and attack by genotoxic agents. The induction of chromosomal alterations may be taken to indicate genetic damage as well. For the localization of chromosomal alterations, karyotypes with marker chromosomes are required. Strains of yeast have been utilized in vitro as indicators of reverse mutations, gene conversion, mitotic recombination, aneuploidy, and other forms of chromosome damage. The primary changes induced by X-rays include structural alterations of chromosomes following breakage and rejoining. Some drugs have also been observed to induce chromosome damage in humans, including daunomycin. Some common cell lines in use are Syrian hamster embryo, Chinese hamster ovary, and human diploid fibroblasts coupled to an external metabolic activation system. In the former, certain characteristic features are observed: certain vital processes are switched off, but enough metabolic activities are retained, which permit the tissue to recover when the external stimulus is removed.