What is a point mutation?

A point mutation refers specifically to a change in a single nucleotide within the DNA sequence. This type of mutation can occur in various forms, such as a substitution, insertion, or deletion of a nucleotide base. Because it impacts only one nucleotide, point mutations can have different effects on gene expression and protein function depending on where they occur and how they alter the genetic code. For instance, a substitution might change one amino acid in a protein, which can lead to different phenotypic outcomes in an organism.

Other options pertain to mutations that involve larger-scale changes in the genome. A mutation affecting an entire chromosome or multiple genes would involve more extensive alterations in the DNA structure and typically falls under categories such as chromosomal mutations or larger genomic rearrangements. Additionally, the option that suggests a mutation occurs only in RNA restricts the definition of mutations prematurely, as mutations are primarily discussed in the context of DNA, though they can also influence RNA. Thus, point mutations are distinct because they are specifically about the alteration of a single nucleotide, making option C the clear and correct choice.