Evolution of a normal karyotype in a mouse bladder epithelial cell line transformed in vitro

An in vitro transformed, carcinoma-producing mouse bladder epithelial cell line with an apparently normal karyotype is described. This cell line has arisen as a variant from a cell line that was trisomic for chromosome #15. It was suggested that the malignant phenotype in the parental cell line results from an excess of "abnormal" chromosomes. A mechanism is discussed for the evolution of an apparently normal karyotype from an abnormal karyotype.