mutation, in biology, a sudden, random change in a gene, or unit of hereditary material, that can alter an inheritable characteristic. Most mutations are not beneficial, since any change in the delicate balance of an organism having a high level of adaptation to its environment tends to be disruptive. As the environment changes, however, mutations can prove advantageous and thus contribute to evolutionary change in the species. In higher animals and many higher plants a mutation may be transmitted to future generations only if it occurs in germ, or sex cell, tissue; somatic, or body cell, mutations cannot be inherited except in plants that propagate asexually (see reproduction). Sometimes the word mutation is used broadly to include variations resulting from aberrations of chromosomes; in chromosomal mutations the number of chromosomes may be altered, or segments of chromosomes may be lost or rearranged. Changes within single genes, called point mutations, are actual chemical changes to the structure of the constituent DNA.
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