Which mutation involves insertion or deletion that shifts the reading frame?

Which mutation involves insertion or deletion that shifts the reading frame?

• A. Frameshift mutation
• B. Silent mutation
• C. Missense mutation
• D. Nonsense mutation

Answer: (A)

Frameshift mutations occur when nucleotides are inserted or deleted in a way that changes the downstream grouping of codons. Because the genetic code is read three nucleotides at a time, adding or removing bases shifts every codon from the point of mutation onward, producing a string of incorrect amino acids and often an early stop signal. The resulting protein is usually garbled and nonfunctional. If the indel is a multiple of three, the reading frame stays intact, leading to an in-frame addition or loss of amino acids rather than a full frame shift. Silent mutations keep the amino acid sequence the same, missense mutations change one amino acid to another without shifting the frame, and nonsense mutations create a premature stop codon, truncating the protein—none of these involve shifting the reading frame in the way a frameshift mutation does.

Frameshift mutations occur when nucleotides are inserted or deleted in a way that changes the downstream grouping of codons. Because the genetic code is read three nucleotides at a time, adding or removing bases shifts every codon from the point of mutation onward, producing a string of incorrect amino acids and often an early stop signal. The resulting protein is usually garbled and nonfunctional. If the indel is a multiple of three, the reading frame stays intact, leading to an in-frame addition or loss of amino acids rather than a full frame shift. Silent mutations keep the amino acid sequence the same, missense mutations change one amino acid to another without shifting the frame, and nonsense mutations create a premature stop codon, truncating the protein—none of these involve shifting the reading frame in the way a frameshift mutation does.