G1 is a resting phase; during S phase, DNA synthesis takes place and G2 phase is again a resting phase following DNA synthesis. These three phases viz. G1, S and G2 constitute interphase, while the main mitotic division takes place during M phase. Durations of different phases vary not only in different materials, but also in different tissues of the same organism. These may also vary in cells in culture using different culture media. The durations of different phases in three materials are given in Table 7.1. The mitotic phase consists of the following stages :
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