For a long time, cytologists considered interphase the period between two consecutive divisions- as “resting phase”. But cells spend most of their life span in interphase as well as intense biosynthetic activity occurs during this period. Replication of nuclear DNA usually occurs in the S-period which is preceeded and followed by two gap periods designated as G1 and G2 phase respectively. G1 and G2 provide additional time for growth, the former takes a decisive step that commits it to DNA replication and completion of division cycle. While G2 phase provides a safety gap allowing the cell to ensure DNA replication has completed before mitosis.