A permanent transmissible change in genetic material, usually in a single gene. A mutation occurs when a DNA gene is damaged or changed in such a way as to alter the genetic message. This change may occur within a gene or involve larger regions of a chromosome. Mutations within single genes are actual chemical changes to the nucleotide sequences of the constituent DNA. In chromosomal mutations, the number of chromosomes may be altered, or segments of chromosomes may be lost, amplified or rearranged. Mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses, or can occur deliberately under cellular control during the processes such as meiosis or hypermutation. In multicellular organisms, mutations can be subdivided into germline mutations, which can be passed on to progeny and somatic mutations, which (when accidental) often lead to the malfunction or death of a cell and can cause cancer. Some germline mutations result in adaptive advantages for species survival, and are considered to be the driving force of evolution.

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