Which mutation results in a codon that encodes the same amino acid as the original sequence?

Which mutation results in a codon that encodes the same amino acid as the original sequence?

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

Answer: (A)

Mutations that don’t change the amino acid are possible because the genetic code is degenerate: multiple codons can specify the same amino acid. A silent mutation is a point change in the DNA that yields a synonymous codon, so the amino acid sequence stays the same. This often happens when the change occurs in the third position of a codon, where wobble base pairing allows different nucleotides to encode the same amino acid. For example, a codon for a given amino acid might be UUU or UUC, both producing the same amino acid; a change between them is silent. In contrast, a missense mutation would replace one amino acid with a different one, altering the protein sequence. A nonsense mutation would create a premature stop codon, truncating the protein. A frameshift mutation would shift the reading frame, changing all downstream amino acids and typically ruining the protein.

Mutations that don’t change the amino acid are possible because the genetic code is degenerate: multiple codons can specify the same amino acid. A silent mutation is a point change in the DNA that yields a synonymous codon, so the amino acid sequence stays the same. This often happens when the change occurs in the third position of a codon, where wobble base pairing allows different nucleotides to encode the same amino acid. For example, a codon for a given amino acid might be UUU or UUC, both producing the same amino acid; a change between them is silent.

In contrast, a missense mutation would replace one amino acid with a different one, altering the protein sequence. A nonsense mutation would create a premature stop codon, truncating the protein. A frameshift mutation would shift the reading frame, changing all downstream amino acids and typically ruining the protein.