The cell cycle is the process by which cells reproduce themselves along with their genetic material, ie, nuclear DNA. The four phases of the cell cycle are G1,S,G2 and M.
[a] G1-phase (first gap phase before DNA replication)?Cell gets decide to differentiate during G1-phase. The differentiated cells that no longer divide are arrested usually in G1 phase, such a type of phase is called G0-phase, set on next phase as appropriate.
[b] S-phase (synthesis phase)?DNA replication occurs. Protein molecules called histones are synthesized and cover each DNA strand. Each chromosome divides into two chromatids. At this stage the cell is 4n.
[c] G2-phase (second gap phase before mitosis) ? intensive cellular synthesis mitochondria and chloroplasts divide, energy store increase, mitotic begin to form. [d] M-phase (mitotic phase)? nuclear division in four stages and cytoplasmic division.