Significance of Mitosis

Mitosis is frequently described as an 'equational division' because the number of chromosomes in each of the two daughter cells it produces is exactly the same as the number in the original parent cell, and because the genetic content of the daughter cells is, in the ordinary course of events, identical both to that of the parent cell and to each other -- the equation of chromosome number and genetic content is preserved rather than changed. This single defining property is what makes mitosis suited to a wide range of essential biological roles.

The most obvious role of mitosis is growth. A multicellular organism does not grow by its individual cells swelling indefinitely in size; instead, growth occurs overwhelmingly through repeated rounds of mitotic cell division, which increase the total number of cells that make up the body. Because every new cell produced by mitosis carries a complete, identical copy of the genome, the tissue that results remains uniform in its genetic instructions even as it increases enormously in cell number, from the single fertilised egg of an animal to the many trillions of cells of an adult body.

A closely related role is the repair and replacement of damaged or worn-out cells. Throughout the life of an organism, cells in many tissues are continuously lost -- skin cells are shed and replaced, the lining of the gut is renewed at a rapid pace, and blood cells have a limited lifespan and must be continuously replenished. Mitotic division in the appropriate stem-cell or progenitor populations supplies fresh replacement cells that are genetically identical to the cells they replace, so that the tissue's structure and function are maintained without alteration. The same process underlies wound healing, where localised, accelerated mitotic division at the site of an injury produces the new cells needed to close and repair the damaged tissue.

Mitosis is also the basis of asexual reproduction in many organisms. In single-celled organisms such as Amoeba and yeast, mitotic division of the parent cell directly produces new, independent individuals. In many plants, vegetative propagation from a stem cutting, a bulb or a runner likewise depends on repeated mitotic divisions to build the tissues of the new plant, each cell of which is genetically identical to the parent plant from which it arose -- which is why plants propagated this way are described as clones of the parent. …