Fig. 4. Timing and variability of cell cycle phases. Cell cycle analysis was performed on whole cycles of Dictyostelium cells expressing GFP-PCNA, in asynchronous culture. (A) Distribution of cell cycle timing for early S, late S and G2. (B) Frequency distribution of G2 variation between sister cells, representing the time cells remain in G2 after their sister has divided. Includes exponential fit. (C,D) Frequency distributions of S variation between sisters, representing the time cells remain in early (C) or late (D) S phase after their sister has finished dividing. Random pair comparisons are shown on the right.