nonsense mutation(redirected from Codon, nonsense)
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1. a second mutation that alters the anticodon in a tRNA so that it can recognize a nonsense (stop) codon, thus suppressing termination of the amino acid chain. Compare: amber mutation, ochre mutation, umber mutation.
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).
Synonym(s): nonsense mutation
a mutation in which one of the three terminator codons in the mRNA used to signal the end of a polypeptide appears in the middle of a genetic message and causes premature termination of transcription and release of incomplete, generally nonfunctional polypeptides from the ribosome. The three types are amber mutation, ochre mutation, opal mutation.
nonsense mutationA POINT MUTATION which changes a CODON that specifies an amino acid into a termination codon-one that marks the position where translation of a messenger RNA sequence should stop. The result is a gene with a segment lopped off. Such a gene will code for a protein that may have missing amino acids and may thus be functionally defective.
nonsense mutationan alteration in a DNA POLYNUCLEOTIDE CHAIN that results in a NONSENSE CODON when transcribed on to mRNA.
1. a nucleotide change, including base substitutions, insertions or deletions in DNA, or RNA in the case of some viruses, that gives rise to the mutant phenotype.
2. an animal exhibiting such change. Called also a sport.
see reverse mutation (below).
base substitution mutation
may be a transition in which a purine-pyrimidine pair is substituted by the other purine-pyrimidine pair, or transversion in which a purine-pyrimidine pair is replaced by one of the two pyrimidine pairs.
chain termination mutation
one in which the new base sequence introduces a stop codon and thereby prematurely terminates synthesis of the polypeptide; the three mutations are also called amber (UAG), ochre (UAA) and opal (UGA).
one produced by loss of nucleotides from a DNA sequence.
frame shift mutation
occur as a result of either the insertion of a new base pair or the deletion of a base pair or a block of base pairs from the DNA base sequence; these, unless they occur in 3 or multiples of 3, are most serious in that the message to the right of the frame shift is garbled.
one in which the amino acid substitution only partially disrupts the function of the protein; in bacteria this is usually manifested by reduced growth rate.
one causing an amino acid substitution in the protein.
one in which a stop codon is substituted for a codon that specifies an amino acid.
operator constitutive mutation
one or more base changes in the operator region (originally defined for the lactose operon) which stop the repressor protein from tightly binding to sequence such that it is less effective in preventing RNA polymerase from inhibiting transcription.
a single changed base pair in the DNA of an organism which may be a base substitution, base insertion or base deletion.
the frequency of mutations in the population over time.
in regulation of gene expression, a mutation in the repressor protein that decreases the binding affinity of the repressor protein for the operator which leaves the gene permanently turned on.
one in which the wild-type phenotype is restored; such organisms are called revertants. Called also back mutation, reversion mutation.
see suppressor mutation.
one in which there is a base change but because of the redundancy of the genetic code the same amino acid is coded, or one in which there is an amino acid substitution in the protein which has no detectable effect on the phenotype.
a change in the DNA sequence that occurs in somatic cells, i.e. not gametes. The mechanism underlying the generation of diversity of antigen recognition by immunoglobulins and T cell receptor molecules. The fundamental cause of cancer, in which the mutation occurs spontaneously or is induced by carcinogens, such as sunlight, chemicals or viruses.
a particular type of reversion mutation in which a mutation at a second site restores the original phenotype; most simply a mutation produced by a base deletion may be restored to wild type by a proximate but independent base substitution. Called also second-site mutation.
temperature-sensitive (ts) mutation
one in which there is an altered protein that is active at one temperature, typically 86°F (30°C) and inactive at a higher temperature, usually 104 to 108°F (40 to 42°C), e.g. ts mutant virus and bacteria.
occur in genes producing diffusible products, in contrast to cis-dominant mutation in which mutations occur in regulatory sequences that are recognized by other proteins.
one in which the base change does not change the pyrimidine-purine orientation. See also base substitution mutation (above).
one produced by the insertion of a transposable genetic element.
one in which the purine-pyrimidine orientation is changed to pyrimidine-purine or vice versa. See also base substitution mutation (above).