What is the first event that happens in the original cell?

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The cell cycle is divided in two main events : interphase and mitosis. However, those two phases have further sub-divisions.

Interphase
During interphase, the cell copies its DNA in preparation for mitosis. This phase is divided into 3 shorter phases : G1, S and G2.

G1 : During this phase, the cell grows in preparation for DNA replication. Cellular components such as organelles and centrosomes are replicated.

S : S is the phase where the DNA packed into chromosomes is duplicated. Replication of DNA by a certain enzyme is essential as it allows each cell created by the division to have the exact same genetic make-up. At the end of this phase, the cell contains twice its genetic material.

G2 : During this phase, a certain enzyme checks and corrects any error in the duplication of the genetic material.

Mitosis
During mitosis, the cell is split into two independent and identical cells. Mitosis is divided into 4 shorter phases : prophase, metaphase, anaphase and telophase.

Prophase : The chromosomes start to condense and the nucleolus disappears. The nuclear envelope breaks down.

Metaphase : Chromosomes align at the metaphase plate which is the centre of the cell.

Anaphase : Chromatids of each chromosome are separated and start migrating towards opposite poles of the cell.

Telophase : Nuclear membranes reappears, one for each set of chromosomes. Chromosomes decondense.

Cytokinesis
Cytokinesis is the division of the cytoplasm to form two cells. In the case of an animal cell, the cell is pinched in two, it is called cleavage furrow. In the case of plant cells, the cell plate forms down the middle of the cell, splitting it into two daughter cells.