The chromatid gap--a useful parameter in genotoxicology?

Chromatid gaps occur as two morphologically indistinguishable types--the clastogenic (DNA damage) type and the turbagenic (no DNA damage) type--and are induced by many genotoxins in a dose-dependent way. Gaps may serve as a low-dose sentinel parameter in genotoxicology. However, their usefulness is limited until further studies have shown whether the turbagenic substances that cause gaps are all capable of inducing segregational errors. In genetic toxicology testing and monitoring, methanol/acetic acid-fixed and air-dried preparations are stained in Giemsa and are then studied under the light microscope. With this method gaps and breaks cannot be distinguished unambiguously and should therefore be scored in the same class of aberrations.