During interphase, the cell is preparing to divide and is actively synthesizing the required components. Originally and inaccurately referred to as "the resting stage," the interphase is actually a period in which a considerable degree of activity is taking place on the sub-cellular and molecular level. Prior to division, the cell must first manufacture the required materials and duplicate its chromosomes, which are activities that represent the primary function of the interphase stage.
The interphase is divided into three subdivisions: G1 (gap one), S (synthesis) and G2 (gap two). During G1, the cell manufactures a range of proteins that are required for DNA replication. The chromosomes are then replicated during the S stage. Each replicated chromosome consists of two sister chromatids, thus effectively doubling the cell's DNA. The chromosome count, or ploidy, however, remains the same. In the following G2 phase, the cell manufactures those proteins and structures that will be required for the upcoming division. This process of division is called mitosis or, if sexual reproduction is involved, meiosis.
The amount of time a cell spends in interphase and its subdivisions is dependent upon the species of organism and the type of cell. The duration of the interphase stage for the majority of adult mammals is about 20 hours and represents about 90 percent of the time spent during cell division.