Which of the following best describes a gene mutation?

A gene mutation is best described as an alteration to the base sequence in DNA. This definition accurately captures the essence of what a gene mutation is, as it specifically involves changes to the nucleotide sequence that make up a gene. These alterations can lead to changes in protein structure and function, impacting the traits expressed by an organism.

Mutations can occur in various ways, including substitutions, deletions, insertions, or duplications of nucleotides. Each of these types of alterations can have different implications for gene function and expression. For instance, a substitution might lead to a different amino acid in a protein, potentially altering its function, whereas a deletion might result in a frameshift that changes the entire protein.

The other options describe different biological concepts. A reversible change in DNA suggests that the alteration can be undone, while gene mutations are typically permanent changes in the genetic code. A change affecting multiple genes implies a broader scope than what a single gene mutation encompasses, as it does not describe a mutation affecting the sequence of just one gene. A structural change in chromosomes refers to alterations at the chromosomal level, such as translocations or aneuploidy, which are different from the specific DNA sequence change that defines a gene mutation.