Mitosis and Cell Division
Mitosis and Cell
Division
All cells arise from the division of preexisting cells. All the cells found in most multicellular organisms originated from the division of a single cell, the zygote, which is the product of union (fertilization) of an egg and a sperm (the gametes). Cell division provides the basis for one form of growth, for both sexual and asexual reproduction, and for the transmission of hereditary qualities from one cell generation to another cell generation.
In the formation of body cells (somatic cells) the process of nuclear division is referred to as mitosis. By mitosis each “daughter cell” is ensured of receiving a complete set of genetic instructions. Mitosis is a delivery system for distributing the chromosomes and the DNA they contain to continuing cell generations. As an animal grows, its somatic cells differentiate and assume different functions and appearances because of differential gene action. Even though most of the genes in specialized cells remain silent and unexpressed throughout the lives of those cells, every cell possesses a complete genetic complement. Mitosis ensures equality of genetic potential; later, other processes direct the orderly expression of genes during embryonic development by selecting from the genetic instructions that each cell contains. (These fundamental properties of cells of multicellular organisms are discussed further in Principles of Development.)
In animals that reproduce asexually, mitosis is the only mechanism for the transfer of genetic information from parent to progeny. In animals that reproduce sexually, the parents must produce sex cells (gametes or germ cells) that contain only half the usual number of chromosomes, so that the offspring formed by the union of the gametes will not contain double the number of parental chromosomes. This requires a special type of reductional division called meiosis, described in Principles of Genetics:A Review.
All cells arise from the division of preexisting cells. All the cells found in most multicellular organisms originated from the division of a single cell, the zygote, which is the product of union (fertilization) of an egg and a sperm (the gametes). Cell division provides the basis for one form of growth, for both sexual and asexual reproduction, and for the transmission of hereditary qualities from one cell generation to another cell generation.
In the formation of body cells (somatic cells) the process of nuclear division is referred to as mitosis. By mitosis each “daughter cell” is ensured of receiving a complete set of genetic instructions. Mitosis is a delivery system for distributing the chromosomes and the DNA they contain to continuing cell generations. As an animal grows, its somatic cells differentiate and assume different functions and appearances because of differential gene action. Even though most of the genes in specialized cells remain silent and unexpressed throughout the lives of those cells, every cell possesses a complete genetic complement. Mitosis ensures equality of genetic potential; later, other processes direct the orderly expression of genes during embryonic development by selecting from the genetic instructions that each cell contains. (These fundamental properties of cells of multicellular organisms are discussed further in Principles of Development.)
In animals that reproduce asexually, mitosis is the only mechanism for the transfer of genetic information from parent to progeny. In animals that reproduce sexually, the parents must produce sex cells (gametes or germ cells) that contain only half the usual number of chromosomes, so that the offspring formed by the union of the gametes will not contain double the number of parental chromosomes. This requires a special type of reductional division called meiosis, described in Principles of Genetics:A Review.
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