In mitosis, the cell cycle consists of long interphase followed by a short mitotic or M-phase. Interphase is the phase between two successive cell divisions. It is a metabolically very active phase because of the biosynthesis of a number of molecules. It is divided into G1, S and G2 phases/sub-stages. The M phase starts with the nuclear division, corresponding to the separation of daughter chromosomes (karyokinesis) and usually ends with the division of cytoplasm (cytokinesis). G1 phase is also called the growth phase or post-mitotic phase.

G1 phase is the longest phase of interphase; the maximum increase in the cell size occurs during this phase. In this phase, there is an active synthesis of RNA and proteins. G1 phase is the interval between the M and S phases.