A permanent change, a structural alteration, in the DNA or RNA. In humans and many other organisms, mutations occur in DNA. However, in retroviruses like HIV, mutations occur in RNA which is the genetic material of retroviruses. In most cases, such changes are neutral and have no effect or they are deleterious and cause harm, but occasionally a mutation can improve an organism's chance of surviving and of passing the beneficial change on to its descendants. Mutations are the necessary raw material of evolution. Mutations can be caused by many factors including environmental insults such as radiation and mutagenic chemicals. Mutations are sometimes attributed to random chance events. For more information about specific kinds of mutations, see: {{}}Mutation, acquired Mutation, germline Mutation, hereditary Mutation, missense Mutation, nonsense Mutation, null Mutation, point Mutation, private Mutation, somatic
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1. A change in the chemistry of a gene that is perpetuated in subsequent divisions of the cell in which it occurs; a change in the sequence of base pairs in the chromosomal molecule. 2. De Vries term for the sudden production of a species, as distinguished from variation. [L. muto, pp. -atus, to change]
- addition m. SYN: reading-frame-shift m..
- addition-deletion m. SYN: reading-frame-shift m..
- amber m. a m. that results in the formation of the codon UAG, which results in the premature termination of a polypeptide chain. Cf.:suppressor m..
- back m. reversion of a gene to an ancestral form due to further m. to the original codon or one coding for the same amino acid. SYN: reverse m..
- deletion m. SYN: reading-frame-shift m..
- frame-shift m. SYN: reading-frame-shift m..
- induced m. a m. caused by exposure to a mutagen.
- lethal m. a mutant trait that leads to a phenotype incompatible with effective reproduction.
- missense m. a m. in which a base change or substitution results in a codon that causes insertion of a different amino acid into the growing polypeptide chain, giving rise to an altered protein. [mis-sense by analogy with non-sense]
- natural m. SYN: spontaneous m..
- neutral m. a m. with a negligible impact on genetic fitness.
- new m. redundant term for a heritable trait present in the offspring but in neither parent, i.e., not a pre-existing mutant form inherited.
- nonsense m. SYN: suppressor m..
- ochre m. a m. yielding the termination codon UAA, resulting in premature termination of a polypeptide chain. Cf.:suppressor m..
- opal m. SYN: umber m..
- point m. a m. that involves a single nucleotide; it may consist of loss of a nucleotide, substitution of one nucleotide for another, or the insertion of an additional nucleotide.
- reading-frame-shift m. a m. that results from insertion or deletion of a single nucleotide into, or from, the normal DNA sequence; since the genetic code is read three nucleotides at a time, all nucleotide triplets distal to the m. will be one step out of phase and misread, and hence translated as different amino acid s. SYN: addition m., addition-deletion m., deletion m., frame-shift m..
- reverse m. SYN: back m..
- silent m. the form of a genetic trait distinguishable at the genotypic level but not at the level of arbitrary phenotype ( e.g., clinical, immunological, or electrophoretic).
- site specific m. an alteration of the structure of a gene at a specific sequence, usually referring to experimentally produced changes in gene sequence.
- somatic m. a m. occurring in the general body cells (as opposed to the germ cells) and hence not transmitted to progeny.
- spontaneous m. a m. that arises naturally and not as a result of exposure to mutagens. SYN: natural m..
- suppressor m. 1. a second m. that alters the anticodon in a tRNA so that it can recognize a nonsense (stop) codon, thus suppressing termination of the amino acid chain. Cf.:amber m., ochre m., umber m.. 2. genetic changes such that the effect of a m. in one place can be masked by a second m. in another location. There are two types: intergenic suppression (occurring in a different gene) and intragenic suppression (occurring in the same gene but at a different site). SYN: nonsense m..
- transition m. a point m. involving substitution of one base-pair for another, i.e., replacement of one purine for another and of one pyrimidine for another pyrimidine without change in the purine-pyrimidine orientation.
- transversion m. a point m. involving base substitution in which the orientation of purine and pyrimidine is reversed, in contradistinction to transition m..
- umber m. a m. yielding the termination codon UGA, resulting in premature termination of a polypeptide chain. Cf.:suppressor m.. SYN: opal m..
- up promoter m. a m. that increases the frequency of initiation of transcription.

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mu·ta·tion myü-'tā-shən n
1) a relatively permanent change in hereditary material involving either a physical change in chromosome relations or a biochemical change in the codons that make up genes also the process of producing a mutation
2) an individual, strain, or trait resulting from mutation
mu·ta·tion·al -shnəl, -shən-əl adj
mu·ta·tion·al·ly adv

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a change in the genetic material (DNA) of a cell, or the change this causes in a characteristic of the individual, which is not caused by normal genetic processes. In a point (or gene) mutation there is a change in a single gene; in a chromosome mutation there is a change in the structure or number of the chromosomes. All mutations are rare events and may occur spontaneously or be caused by external agents (mutagen). If a mutation occurs in developing sex cells (gametes) it may be inherited. Mutations in any other cells (somatic mutations) are not inherited.

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mu·ta·tion (mu-taґshən) [L. mutatio, from mutare to change] 1. in genetics, a permanent transmissible change in the genetic material, usually in a single gene, although the term is sometimes used to include gross alterations in chromosomal structure. 2. a cell, virus, or organism exhibiting such a change.

Medical dictionary. 2011.

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