Which statement best describes a frameshift mutation?

• A. A single-nucleotide substitution that changes one amino acid but does not alter the reading frame (missense mutation)
• B. A mutation in which a DNA segment is reversed in orientation within the chromosome (inversion)
• C. A point mutation that converts a sense codon into a stop codon, prematurely terminating translation (nonsense mutation)
• D. An insertion or deletion of nucleotides not in multiples of three that shifts the mRNA codon reading frame, often altering all downstream amino acids

Answer: (D)

Verified step by step guidance

1. Understand that a frameshift mutation involves changes in the DNA sequence that affect the reading frame of the mRNA during translation.
2. Recall that the genetic code is read in triplets of nucleotides called codons, each coding for a specific amino acid.
3. Recognize that insertions or deletions (indels) of nucleotides in numbers not divisible by three will shift the grouping of these triplets, changing every codon downstream of the mutation.
4. Contrast this with other mutations: missense mutations change one amino acid without shifting the frame, inversions reverse a DNA segment without necessarily affecting the reading frame, and nonsense mutations introduce a premature stop codon.
5. Conclude that a frameshift mutation is best described as an insertion or deletion of nucleotides not in multiples of three that shifts the mRNA codon reading frame, often altering all downstream amino acids.