S-phase/Synthetic phase
(a) DNA replicates and its amount becomes double (2C→ 4C).
(b) Synthesis of histone proteins.
(c) Euchromatin replicates earlier than heterochromatin.
(d) Synthesis of NHC (non-histone chromosomal proteins).
(e) Each chromosome has 2 chromatids. Amount of DNA doubles but the chromosome number remains constant.