Proliferative capacity and DNA content of aging human diploid cells in culture: A cytophotometric and autoradiographic analysis

Using a combination of DNA‐cytophotometry and tritiated thymidine‐autoradiography, we have shown that the majority of nondividing cells in serially propagated human diploid cell populations have the 2C DNA content consistent with their being arrested in the G 1 phase of the diploid cell cycle. Unlabeled 4C cells appear increasingly with time in culture. These may be arrested G 2 diploids or they may be G 1 tetraploids, since there is an associated increase in polyploidy in older cultures as evidenced by the appearance of labeled 8C cells.