How are cells formed?

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New cells are formed from preexisting cells through mitosis. Sexually reproducing organisms also create a type of cell, called a gamete, through meiosis. This phenomenon is one of the principles of the cell theory.

Mitosis is one of the forms of cellular reproduction. 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. The 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 (equator) 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 two daughter (new) cells. 

Meiosis is a similar process but includes two occurrences (known as meiosis I and meiosis II) of cell division to produce four daughter cells. A major difference of meiosis is that it involves the exchange of DNA between chromosomes during prophase in meiosis I, known as recombination, ending with four genetically diverse daughter cells. The purpose of meiosis is to create gametes. Sexual reproduction involves the joining of a female and a male gamete.

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