Which statement best describes a frameshift mutation?

• A. A point mutation that changes a codon into a stop codon, prematurely terminating translation without shifting the reading frame
• B. A single-nucleotide substitution that changes one codon to a different codon but does not alter the reading frame
• C. An insertion or deletion of nucleotides in a coding sequence that is not in multiples of three, shifting the mRNA codon reading frame and often altering all downstream amino acids
• D. A chromosomal rearrangement in which a segment of one chromosome is reversed in orientation, typically without changing the codon reading frame within a gene

Answer: (C)

Verified step by step guidance

1. Understand that a frameshift mutation specifically involves changes in the nucleotide sequence that alter 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 one amino acid, so insertions or deletions not in multiples of three will shift this reading frame.
3. Recognize that a frameshift mutation results from insertions or deletions of nucleotides that are not multiples of three, causing all downstream codons to be read incorrectly and often producing a nonfunctional protein.
4. Differentiate frameshift mutations from point mutations, which involve single-nucleotide substitutions that may change one codon but do not shift the reading frame.
5. Note that chromosomal rearrangements like inversions change the order of segments but typically do not affect the reading frame within a gene, so they are not frameshift mutations.