| 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) |
| transversion mutation | A point mutation involving base substitution in which the orientation of purine and pyrimidine is reversed, in contradistinction to transition mutation. (05 Mar 2000) |
| umber mutation | A mutation yielding the termination codon UGA, resulting in premature termination of a polypeptide chain. Compare: suppressor mutation. Synonym: opal mutation. (05 Mar 2000) |
| unstable mutation | <molecular biology> A mutation that has a high likelihood of reverting to its original form. (13 Nov 1997) |
| up mutation | <molecular biology> Refers to any mutation in the promoter region of a gene which can trigger transcription initiation. (09 Oct 1997) |
| up promoter mutation | A mutation that increases the frequency of initiation of transcription. (05 Mar 2000) |
| forward mutation | Any mutation which renders a formerly functional gene nonfunctional. Compare: back mutation. (09 Oct 1997) |
| frameshift mutation | <molecular biology> A type of mutation that results from insertion or deletion of a single nucleotide into, or from, an open reading frame in the normal DNA sequence. Normally, the genetic code is read in the wrong frame, three nucleotides at a time, and the entire sequence downstream of the mutation, is translated into a polypeptide with a garbled amino acid sequence from the mutated codon onwards. These mutations may be induced by certain types of mutagens or may occur spontaneously and usually result in the generation, downstream, of nonsense, chain termination codons. Synonym: addition mutation, addition-deletion mutation, deletion mutation, reading-frameshift mutation. (21 Jun 2000) |
| lethal mutation | <genetics, molecular biology> Mutation that eventually results in the death of an organism carrying the mutation. (18 Nov 1997) |
| Abbe theory of image formation | <optics, physics> Abbe's theory is based on the fact that a non-self-luminous particle, which is illuminated by an extraneous source, gives rise to diffracted light rays, in addition to the dioptric pencil. He stated that to form a good microscopical image as many of the diffracted rays as possible should be intercepted by the objective. With closely ruled lines, his theory is easily demonstrated by observing the back lens of the objective, for here the diffracted rays can be observed directly if the aperture diaphragm is closed. It can be shown that, when the illumination is arranged to exclude the diffracted images, resolution is lost. (11 Mar 1998) |