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Silent mutations, also called synonymous or samesense mutations, are mutations in DNA that do not have an observable effect on the organism's phenotype. The phrase silent mutation is often used interchangeably with the phrase synonymous mutation ; however, synonymous mutations are not always silent, nor vice versa.
Point substitution mutations of a codon, classified by their impact on protein sequence. A synonymous substitution (often called a silent substitution though they are not always silent) is the evolutionary substitution of one base for another in an exon of a gene coding for a protein, such that the produced amino acid sequence is not modified.
An example would be a seemingly silent mutation in the multidrug resistance gene 1 , which codes for a cellular membrane pump that expels drugs from the cell, can slow down translation and allow the peptide chain to fold into an unusual conformation, causing the mutant pump to be less functional (in MDR1 protein e.g. C1236T polymorphism changes ...
Many mutations are silent mutations, causing no visible effects at all, either because they occur in non-coding or non-functional sequences, or they do not change the amino-acid sequence due to the redundancy of codons. [33] Some mutagens can cause aneuploidy and change the number of chromosomes in the cell. They are known as aneuploidogens. [34]
This view is based in part on the degenerate genetic code, in which sequences of three nucleotides may differ and yet encode the same amino acid (GCC and GCA both encode alanine, for example). Consequently, many potential single-nucleotide changes are in effect "silent" or "unexpressed" (see synonymous or silent substitution). Such changes are ...
A nucleotide substitution at a 4-fold degenerate site is always a synonymous mutation with no change on the amino acid. [2]: 521–522 A less degenerate site would produce a nonsynonymous mutation on some of the substitutions. An example (and the only) 3-fold degenerate site is the third position of an isoleucine codon.
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A site in a protein-coding sequence of DNA is nonsynonymous if a point mutation at that site results in a change in the amino acid, resulting in a change in the organism's phenotype. [3] Typically, silent mutations in protein-coding regions are used as the "control" in the McDonald–Kreitman test.