GENETICS AND EVOLUTION
MOLECULAR BASIS OF INHERITANCE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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It has no effect on the amino acid sequence of the encoded protein.
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It alters the reading frame of the mRNA.
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It introduces a premature stop codon into the mRNA.
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It changes an amino acid in the encoded protein.
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Detailed explanation-1: -A nonsense mutation occurs in DNA when a sequence change gives rise to a stop codon rather than a codon specifying an amino acid. The presence of the new stop codon results in the production of a shortened protein that is likely non-functional.
Detailed explanation-2: -As noted earlier, a nonsense mutation occurs when a codon for an amino acid is changed to a stop codon. This results in a truncated and usually nonfunctional protein. Such a defect may be suppressed, at least partially, by changing the anticodon sequence of a tRNA molecule so that it recognizes the stop codon instead.
Detailed explanation-3: -In most cases, the primary mechanism whereby a nonsense mutation has an effect is through the degradation of that mRNA by a surveillance mechanism called nonsense-mediated mRNA decay (NMD) and not through translation of the mutant mRNA into a truncated protein (for reviews see[2–6]).
Detailed explanation-4: -Mutations can occur in noncoding regions of a gene and can affect the manner in which exons are removed from an mRNA product. If a mutation introduces a premature stop codon into an mRNA sequence, the: protein will be smaller.
Detailed explanation-5: -Premature stop codons are those that are present in mRNA prior to their normal position in the gene. This means that the message to create the protein of interest is incomplete; thus only incomplete (commonly referred to as truncated) protein is formed.