New cells are formed from preexisting cells. This phenomenon is one of the principles of the cell theory. Mitosis is one of the forms of cellular division. Mitosis is a form of asexual reproduction. It is responsible for the growth and repair of somatic (body) cells. Mitosis occurs rather quickly. It is only a part of a cell's life (known as the cell cycle).
Mitosis consists of four stages: prophase, metaphase, anaphase, and telophase. The acronym PMAT is often used to remember the order of these stages.
Right before mitosis occurs (during interphase, the phase in which the cell spends the majority of its life), the DNA replicates. Replication of DNA is needed in order to maintain the number of chromosomes of the parent cell (original cell) after the cell divides.
During prophase, the DNA condenses into chromosomes and the nucleus begins to disappear.
During metaphase, the chromosomes line up at the middle (metaphase plate) of the cell.
The chromosomes pull apart from one another during anaphase.
Finally, during telophase, the cell begins to pinch inward in the middle, the chromosomes begin to unwind, and two nuclei begin to form.
Although not technically a part of mitosis, cytokinesis is a stage of the cell cycle the cuts the cell furrow in order to cut the parent cell into to daughter (new) cells.