[Spontaneous rate of occurrence of 2 characters of the transformation phenotype in a mouse fibroblast culture].

The spontaneous rate of occurrence of two characters of malignant transformation was studied in mouse embryo fibroblasts C3H10T1/2, clone 8. This cell line, though "immortal" in vitro, is characterized by a normal phenotype in respect to many other properties. The spontaneous rate of occurrence of anchorage-independence (aga+) and dense foci on cell monolayer varied in different experiments from 0.65 X 10(-6) to 1.2 X 10(-6) and from 1.2 X 10(-6) to 3.6 X 10(-6) per cell per generation, respectively. The fluctuation test has shown that both characters occur as random spontaneous events. The altered colony morphology proved to be stable in all 28 foci of independent origin tested. In most cases, the morphological transformants were anchorage-independent. It is suggested that the occurrence of the characters studied is due to mutation in a gene with pleiotropic effect.