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Silent mutations, also called synonymous or samesense mutations, ... This is an example of how some silent mutations are not always silent. [25]
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.
These are both examples of a non-conservative (missense) mutation. Silent mutations code for the same amino acid (a "synonymous substitution"). A silent mutation does not affect the functioning of the protein. A single nucleotide can change, but the new codon specifies the same amino acid, resulting in an unmutated protein.
For example, the effect of a nonsense mutation depends on the proximity of the nonsense mutation to the original stop codon, and the degree to which functional subdomains of the protein are affected. [3] As nonsense mutations leads to premature termination of polypeptide chains; they are also called chain termination mutations. [4]
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 ...
Missense mutations in the MeCP2 protein can cause Rett syndrome, otherwise known as the RTT phenotype. [9] T158M, R306C and R133C are the most common missense mutations causing RTT [9]. T158M is a mutation of an adenine being substituted for a guanine causing the threonine at amino acid position 158 being substituted with a methionine [10].
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]
Marfan syndrome is also an example of dominant negative mutation and haploinsufficiency. Lethal mutations result in rapid organismal death when occurring during development and cause significant reductions of life expectancy for developed organisms. An example of a disease that is caused by a dominant lethal mutation is Huntington's disease.