| NTA | natural thymocytotoxic autoantibody; nitrilotriacetic acid; Nurse Training Act |
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| 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) |
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| 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) |