Frameshift mutations shift the reading frame of the genetic message by inserting or deleting a nucleotide.

Frameshift mutations shift the reading frame of the genetic message by inserting or deleting a nucleotide.

• A. A mutation that shifts the reading frame by inserting or deleting a nucleotide.
• B. A mutation that changes a single base pair.
• C. A mutation that duplicates a gene.
• D. A mutation that only affects noncoding regions.

Answer: (A)

Frameshift mutations occur when nucleotides are inserted or deleted, shifting the triplet reading frame used to translate mRNA. Because codons are read in groups of three, adding or removing a single nucleotide changes every downstream codon, often producing a completely different sequence of amino acids and usually a nonfunctional protein. The statement that describes shifting the reading frame by inserting or deleting a nucleotide matches this mechanism exactly, making it the correct choice. In contrast, changing a single base pair is a point mutation affecting one codon but not the reading frame; gene duplication involves copy-number changes rather than frame shifts; and mutations in noncoding regions typically don’t alter the amino acid sequence or reading frame.

Frameshift mutations occur when nucleotides are inserted or deleted, shifting the triplet reading frame used to translate mRNA. Because codons are read in groups of three, adding or removing a single nucleotide changes every downstream codon, often producing a completely different sequence of amino acids and usually a nonfunctional protein. The statement that describes shifting the reading frame by inserting or deleting a nucleotide matches this mechanism exactly, making it the correct choice. In contrast, changing a single base pair is a point mutation affecting one codon but not the reading frame; gene duplication involves copy-number changes rather than frame shifts; and mutations in noncoding regions typically don’t alter the amino acid sequence or reading frame.