Mitosis Is How Cells Make More Cells
Mitosis and meiosis are two types of cells division. Mitosis is cell division that results in the duplication of cells; the daughter cells genetic copies of the parent cell. This cell multiplication allows for replacement of old cells, tissue repair, growth and development.
Growth & Development
You grew from a zygote, or fertilized egg (the fusion of two cells: an egg and a sperm) into an organism with trillions of specialized cells. Mitosis is the process that enabled you to grow and develop after that fateful meeting of ovum and sperm became ‘you’.
Cell Replacement
Cells must divide in order for an organism to grow and develop, but cell division is also required for maintenance, cell turnover and replacement.
Some cell types of your body, once formed, do not undergo much division, like neurons (nerve cells), for example. However, many tissues of your body are composed of cells that have a high turn-over rate. One example is your skin. The epidermis, or top layer, is coated with dead cells constantly being sloughed off and replaced from below by cells of the dermis (the living cells in the layer of skin below the epidermis). If cells of the dermis were not constantly dividing to replace dead cells, your skin would eventually wear out.
Meiosis is Sex Cell (Gamete) Formation
In sexually reproducing organisms, some cells are able to divide by another method called meiosis. This type of cell division results in the production of gametes (eggs or sperm).
Meiosis is much more complex than mitosis. Whereas mitosis involves the duplication and subsequent division of chromosomes, meiosis involves two divisions of genetic material. As is the case in mitosis, in meiosis the cell duplicates its chromosome number prior to beginning cellular division. Then nuclear division, the sorting out of the genetic material, begins, and unfolds over the course of 2 cellular divisions that result in 4 gametes.
Gametes & Gonads
Gametes are haploid (1n) with half the number of chromosomes than the progenitor cell that they arose from. These haploid sex cells arise in specialized reproductive tissue called the gonads. Ovaries (female gonads) and testes (male gonads) are the sites of meiosis.
Fertilization & Development
Sexual reproduction results in the merging of sperm and egg at fertilization, and brings the chromosome count back to the 2n diploid number necessary for a zygote to have complete genetic information; 2 sets of genetic instructions in 23 pairs of chromosomes. As cells divide, the zygote develops and grows into an embryo, fetus and beyond. These 23 pairs of chromosomes are duplicated with every cell division, and are the genetic material inside nearly every cell of the body.
More Information
See the science education website Science Prof Online for more on cell biology, or look to additional Suite101 biology articles, including Mitosis & Meiosis Comparison, Nucleotides & Nucleic Acids, and Prokaryotic & Eukaryotic Cells
Sources
Campbell, N. A. & Reece J. B. (2005) Biology, seventh edition. Pearson Education Inc.
Campbell, N. A., Reece J. B. & Simon, E. (2004) Essential Biology with Physiology. Pearson Education Inc.
Tami Port - Tami Port is a college professor of cell and microbiology and creator of ScienceProfOnline.com, a free science education website.
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