Instability of the duration of G1 phase of Yoshida sarcoma and ascites hepatomas

The durations and coefficients of variance of G1, S and G2 phase were obtained for 8 cell lines of ascites tumours originated from hepatomas in rats, and these were compared. Although changes in the durations of S and G2 phases were small, the duration of G1 phase increased with the cell cycle time. The coefficient of variance of G1 phase was larger than that of S and G2 phases, most remarkedly at short cycle time. It was concluded that the G1 phase is the most unstable as well as the most variable in its duration.