What happens to chromosomes before mitosis?

Before mitosis the cell is in a stage called 'interphase,' Interphase contains G1, S phase, and G2. In G1 the cell grows in size. There is an important G1 checkpoint that cells hit. If they make it past the checkpoint they will continue to S phase and have their DNA replicated, or they will switch to a nondividing state called G0. After a cell completes S phase it enters G2 and continues to grow. The cell then leaves interphase and enters the mitotic phase containing Mitosis and Cytokinesis. In prophase of mitosis the replicated DNA condenses and it ready for division.

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Polymerization reaction