Clastogenic changes may be picked up by carefully studying chromosomal banding patterns in cell materials. The third type of genotoxic effect is aneuploidization which results when intact chromosomes are added or deleted. Chromosomal abnormalities are one of the most easily recognized forms of genotoxic effects because they can be seen under the microscope as changes in the number or structure of chromosomes. Dominant gene mutations are easily recognized because they are always expressed in the individual that carries that gene. Recessive gene mutations are not expressed in offspring unless each parent contributed a recessive gene to the child.
Polygenic disorders depend on a number of genes for expression.
Diabetes and epilepsy are two human diseases that are thought to have polygenic components. These are the most difficult to chart out because so many may be involved. Because the basic mechanism of cancer involves genetic changes in somatic cells, genotoxicity testing is currently used as a screening procedure for potential carcinogenic effects. We already seem to have a high incidence of genetic damage under natural conditions, thus we would not want to introduce any chemical agent into our environment which might increase the rate of mutations in humans. It would be impossible to document human genetic damage due to chemical exposure until long after the exposure had occurred.