Metaphase chromosome anomaly: association with drug resistance and cell-specific products.

Large, homogeneously staining chromosome regions which lack the longitudinal differentiation ordinarily revealed by cytogenetic "banding" methods have been found in antifolate-resistant Chinese hamster cells and also in human neuroblastoma cells established in vitro. The drug-resistant cells are characterized by excessive production of the target enzyme, dihydrofolate reducatase, while the human neuroblastoma cells have phenotypes of normal neuronal cells. The homogeneously staining region appears to represent a novel metaphase chromosome anaomaly which may have functional significance in cells with specialized properties.