The cell cycle is the sequence of all events within a somatic cell that divides it into two equivalent daughter cells (reduplication). This includes an interphase and a mitotic phase. The interphase encompasses the period between two cell divisions (mitoses). It is further subdivided into three phases: the G1-phase, the S-phase and the G2-phase.
The G1-phase (G for gap) begins immediately after mitosis and is characterized by intensive cell growth and a high synthesis of proteins and RNA. In this phase, each chromosome consists of one chromatid or DNA double helix, which means that each pair of chromosomes consists of two chromatids (2C, where C is the number of chromatids per pair of chromosomes). The G1-phase is of variable duration. It continues into the S-phase (S for synthesis), during which DNA is synthesized (replication). At the end of the S-phase, the chromatids of the 46 chromosomes are duplicated (2n 4C). The S-phase is followed by the G2-phase, in which proteins are synthesized. In addition, it is assumed that DNA is checked during this phase and defective sequences are repaired. The G2-phase is followed by cell division, or mitosis (M-stage), which is subdivided into six stages.