G1 Phase: G1 phase is the interval between mitosis and initiation of DNA replication. In this phase, the cell does not synthesize or, replicate DNA but remains metabolically active. The cell grows in size continuously and synthesizes nucleotides, ATP, proteins, amino acids, RNAs etc. (required during S phase). The length of the G1 phase varies from one cell to another. If a cell divides frequently, then it has a shorter G1 phase and if a cell does not divide frequently, then it has a longer G_{1 }phase. Replication of DNA and duplication of histones takes place in S phase.