Therefore, their cell cycles, which lack G1 and G2 phases and checkpoints, are totally controlled by the cytoplasm. The simplest cell cycle reveals the essential minimum of cell-cycle control.

To maintain ploidy, unidirectional progression through the phases of the cell cycle (G1 → S → G2 → M → G1) is essential. To keep cells from regressing, the transitions of the mitotic cell ...

This sequential expression followed the phases of the traditional cell cycle: G0/G1 (the cell grows larger), S (the cell replicates its DNA), and G2/M (the cell prepares for division and then splits).