... to the period of S phase. The latter lasts until all of the DNA has been replicated. The G2 phase is the period of time that separates the S and M phases and during which the cell has two complete diploid sets of chromosomes. During mitosis, or M phase, cell division occurs and segregates one set of diploid chromosomes to each daughter cell. The two gap phases (G1 and G2) serve as more than simple time delays to allow cell growth. They also provide time for the cell to monitor the internal and external environment to ensure that conditions are suitable and preparations are complete before the cell commits itself to the major upheavals of S phase and mitosis. If extracellular conditions are unfavourable, for example, cells delay their progress through G1 and may even enter a specialized resting state known as G0 in which they can remain before resuming ...

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