Which statement defines a point mutation?

• A. A type of mutation that causes a single nucleotide base change, insertion, or deletion of the genetic material, DNA or RNA.
• B. A mutation that doubles the genome.
• C. A mutation that affects only noncoding regions.
• D. A mutation that only affects protein folding.

Answer: (A)

A point mutation is a small-scale change in the genetic sequence that occurs at a single nucleotide position in DNA or RNA. The essence is that the alteration happens at one nucleotide, typically a base substitution where one nucleotide is replaced by another, and it can also include the insertion or deletion of a single nucleotide. This focus on single-nucleotide changes is what defines the concept, distinguishing it from larger-scale changes that affect big chunks of DNA or the entire genome, or from mutations whose description centers on where they occur (noncoding regions) or their phenotypic effect (like protein folding).

The statement captures this idea by describing a mutation that causes a single nucleotide base change, insertion, or deletion, which aligns with the tiny, nucleotide-level scope of point mutations.