Which statement is true about point mutations?

• A. Point mutations can cause a single base change in DNA or RNA.
• B. Point mutations only involve insertions or deletions, not base changes.
• C. Frameshift mutations only occur in noncoding regions.
• D. Nonsense mutations produce amino acid changes.

Answer: (A)

Point mutations are changes at a single nucleotide. This means a single base in the genetic material is altered, which can happen in DNA and, in organisms with RNA genomes, in RNA as well. Because the genetic code translates codons made of three bases, one base change can change the codon to code for a different amino acid, create a stop signal, or sometimes leave the amino acid unchanged if the code is redundant. That single-base alteration is the defining feature of point mutations.

The other statements mix in different kinds of changes. Insertions or deletions affect one or more bases and can shift the reading frame (frameshift mutations), which is not what a point mutation does. Nonsense mutations create stop codons and typically truncate a protein, not simply cause an amino acid substitution. So the statement that correctly describes point mutations is that they involve a single base change in DNA or RNA.