Which mutation type results from insertions or deletions that shift the reading frame?

Which mutation type results from insertions or deletions that shift the reading frame?

• A. Frameshift mutation
• B. Point mutation
• C. Mutagen
• D. Polyploidy

Answer: (A)

The reading frame is the way nucleotides are grouped into codons of three to code for amino acids. When nucleotides are inserted or deleted, the grouping downstream is disrupted. If the insertion or deletion isn’t a multiple of three, every downstream codon shifts, so the amino acid sequence changes dramatically and a premature stop codon is often introduced. That widespread downstream misreading is the hallmark of a frameshift mutation. This kind of mutation arises specifically from insertions or deletions that shift the frame, which is why it’s the correct concept here. For context, a point mutation is a single-nucleotide change that typically preserves the reading frame, so only one codon (or none, if it’s a silent change) is affected. A mutagen is anything that causes mutations, not a type of mutation itself. Polyploidy means more than two complete sets of chromosomes, which is a chromosome-number change, not a shift in codon reading frames.

The reading frame is the way nucleotides are grouped into codons of three to code for amino acids. When nucleotides are inserted or deleted, the grouping downstream is disrupted. If the insertion or deletion isn’t a multiple of three, every downstream codon shifts, so the amino acid sequence changes dramatically and a premature stop codon is often introduced. That widespread downstream misreading is the hallmark of a frameshift mutation. This kind of mutation arises specifically from insertions or deletions that shift the frame, which is why it’s the correct concept here.

For context, a point mutation is a single-nucleotide change that typically preserves the reading frame, so only one codon (or none, if it’s a silent change) is affected. A mutagen is anything that causes mutations, not a type of mutation itself. Polyploidy means more than two complete sets of chromosomes, which is a chromosome-number change, not a shift in codon reading frames.