6. If mutation changes codon in such a way that there is no effect on functioning and sequence of protein. This type of mutation is termed as
(1) Silent mutation (2) Mis-sense
(3) Transition (4) Frameshift
Silent mutation is the correct answer, as it describes a codon alteration that results in no change to the protein’s amino acid sequence or function due to genetic code degeneracy.
Option Analysis
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(1) Silent mutation: This occurs when a nucleotide substitution changes a codon to a synonymous one coding for the same amino acid, preserving protein structure and function entirely.
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(2) Mis-sense: A missense mutation substitutes one amino acid for another, often altering protein function, such as in sickle cell anemia where valine replaces glutamic acid.
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(3) Transition: This refers to a purine-to-purine or pyrimidine-to-pyrimidine base change (e.g., C to T), which may or may not affect the protein; it describes the mutation type, not its functional outcome.
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(4) Frameshift: Insertions or deletions shift the reading frame, garbling the entire downstream amino acid sequence and typically disrupting protein function severely.
Mechanism and Examples
Silent mutations exploit the genetic code’s redundancy, where multiple codons specify the same amino acid; for instance, changing DNA codon TTC (phenylalanine) to TTT keeps the protein unchanged. Though often neutral, rare cases may subtly influence translation speed or mRNA stability, but the core definition holds no primary effect on protein sequence. In exams like CSIR NET, recognizing this distinction tests understanding of point mutations versus their impacts.
