Figure 2. Simplified model for progression through the cell cycle.

The cell cycle is divided into two generalized phases: called interphase and telophase for simplicity. Gene expression occurs during the interphase, while cell division and associated processes occur in the telophase. In the interphase gene expression profile is governed by the stable epigenetic marks on the master-regulatory genes. In the telophase, however, protein environment can change the epigenetic marks of the master-regulaory genes, particularly when DNA is decondensing after cell division. Differentiation signals (newly expressed proteins) determine future epigenetic marks created during telophase due to the action of the new protein environment. The color code representing genetic and epigenetic states is the same as in Fig. 1.