| natural mutation | A mutation which occurs by itself without first being affected by a mutagen, for example during the process of DNA replication. Spontaneous mutations arise at a remarkably constant rate. The rate that spontaneous mutations arise has been used as an evolutionary clock to estimate how closely related two (or more) separate species are to each other. (09 Oct 1997) |
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| neutral mutation | A mutation that has no selective advantage or disadvantage. Considerable controversy surrounds the question of whether such mutations can exist. (18 Nov 1997) |
| new mutation | Redundant term for a heritable trait present in the offspring but in neither parent, i.e., not a pre-existing mutant form inherited. (05 Mar 2000) |
| substitution mutation | A mutation caused by a nucleotide base being replaced by a different one. (09 Oct 1997) |
| nonsense mutation | <molecular biology> A mutation that causes a polypeptide chain to be ended prematurely. (13 Nov 1997) |
| null mutation | Change in a gene that leads to nothing, for example to no enzyme or to a nonfunctioning enzyme. (12 Dec 1998) |
| suppressor mutation | <molecular biology> Mutation that alleviates the effect of a primary mutation at a different locus. May be through almost any mechanism that can give a primary mutation, but perhaps the most interesting class are the amber and ochre supressors, where the anticodon of the tRNA is altered so that it mis reads the termination codon and inserts an amino acid, preventing premature termination of the peptide chain. (18 Nov 1997) |
| deletion mutation | <molecular biology> A mutation in which one or more (sequential) nucleotides is lost by the genome. If the number lost is not divisible by 3 and is in a coding region, the result is a frameshift mutation. (18 Nov 1997) |
| down promoter mutation | <molecular biology> A mutation (a change in base pair sequence) in a promoter region, this results in lower gene expression (less transcription of the gene occurs). (09 Oct 1997) |
| induced mutation | A mutation caused by exposure to a mutagen. (05 Mar 2000) |
| insertion mutation | A mutation caused by the insertion of at least one extra nucleotide basein a DNA sequence. (09 Oct 1997) |
| ochre mutation | Mutation that changes any codon to the termination codon UAA. (18 Nov 1997) |
| opal mutation | <molecular biology> Mutation that changes any codon to the termination codon UGA. (18 Nov 1997) |
| temperature sensitive mutation | <genetics, molecular biology> A type of conditional mutation in organism, somatic cell or virus that makes it possible to study genes whose total inactivation would be lethal. Such ts mutations can also make possible studies of the effect of reversible switching by temperature changes) in expression of the mutated gene. The usual mechanism of temperature sensitivity is that the mutated gene codes for a protein with a temperature dependent conformational instability, so that it possesses normal activity at one temperature (the permissive temperature), but is inactive at a second (nonpermissive) temperature. (18 Nov 1997) |
| transition mutation | A point mutation 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. (05 Mar 2000) |