Which mutation type shifts the reading frame of the genetic code, affecting downstream codons?

Which mutation type shifts the reading frame of the genetic code, affecting downstream codons?

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

Answer: (A)

The reading frame is the way the sequence is partitioned into codons of three nucleotides that specify amino acids. If nucleotides are inserted or deleted in numbers not divisible by three, the grouping of codons shifts for all downstream positions. This changes every amino acid that follows the mutation and often introduces a premature stop, producing a nonfunctional or truncated protein. This is the hallmark of a frameshift mutation. In contrast, a substitution changes one nucleotide within a codon and can alter a single amino acid without shifting the downstream reading frame; a silent mutation is a substitution that does not change the amino acid due to codon redundancy; a nonsense mutation changes a codon to a stop without altering the downstream frame.

The reading frame is the way the sequence is partitioned into codons of three nucleotides that specify amino acids. If nucleotides are inserted or deleted in numbers not divisible by three, the grouping of codons shifts for all downstream positions. This changes every amino acid that follows the mutation and often introduces a premature stop, producing a nonfunctional or truncated protein. This is the hallmark of a frameshift mutation.

In contrast, a substitution changes one nucleotide within a codon and can alter a single amino acid without shifting the downstream reading frame; a silent mutation is a substitution that does not change the amino acid due to codon redundancy; a nonsense mutation changes a codon to a stop without altering the downstream frame.