Define interphase and comment on how much time a typical cell spends in interphase, noting and explaining exceptions to the typical situation.
The first three stages of the cell cycle, G1, S, and G2, are known collectively as the cell's interphase, or the period of time that separates the cell's mitotic divisions. A cell typically spends at least ninety percent of its total cell cycle in interphase. Exceptions include differentiated nerve and heart muscle cells, which normally do not divide and remain arrested in a non-division stage called G0. Cell cycles become arrested in the G1 or G2 stages when certain chemical control signals are absent. These chemical control signals would normally stimulate the cell's passage through certain restriction points in each stage, thereby committing the cell to entering the next stage of the cell cycle.
