Frameshift mutations near the start of a gene typically cause what kind of effect on the resulting protein?

Frameshift mutations near the start of a gene typically cause what kind of effect on the resulting protein?

• A. They often produce a completely unchanged protein.
• B. They cause only a single amino acid change with minimal effect.
• C. They produce a protein with a small, localized change.
• D. They yield a drastically altered amino acid sequence downstream of the mutation.

Answer: (D)

Frameshift mutations shift the reading frame of the genetic code. When this happens near the start of a gene, every codon downstream is read in a new frame, so the amino acids added after the mutation are almost completely different from the original sequence. This usually yields a protein with a drastic change in its amino acid sequence downstream, often accompanied by a premature stop codon that creates a truncated, nonfunctional product. That’s why the outcome is a drastically altered amino acid sequence downstream of the mutation. In contrast, a single amino acid change or a small localized change would come from point mutations or in-frame indels, not from a frameshift.

Frameshift mutations shift the reading frame of the genetic code. When this happens near the start of a gene, every codon downstream is read in a new frame, so the amino acids added after the mutation are almost completely different from the original sequence. This usually yields a protein with a drastic change in its amino acid sequence downstream, often accompanied by a premature stop codon that creates a truncated, nonfunctional product. That’s why the outcome is a drastically altered amino acid sequence downstream of the mutation. In contrast, a single amino acid change or a small localized change would come from point mutations or in-frame indels, not from a frameshift.