Which mutation type results in a permanent change in the DNA sequence of a gene?

A point mutation results in a permanent change in the DNA sequence of a gene because it involves the alteration of a single nucleotide in the sequence. This change can occur in several ways, such as a substitution where one base pair is replaced with another, potentially affecting the protein that is produced by the gene. Because point mutations directly modify the genetic code, they can lead to different traits or functions if they occur within a coding region of a gene.

While gene expression refers to the process by which information from a gene is used to synthesize functional products like proteins, it does not involve a permanent change in the DNA itself. On the other hand, an inversion involves a segment of DNA being flipped within the chromosome, which can affect gene expression but does not create a permanent alteration in the base sequence itself. Deletion, while it does remove part of the DNA sequence, also results in a permanent change similar to a point mutation but is considered a different type of mutation.