What type of mutation occurs naturally, such as an error during DNA replication?

A spontaneous mutation is a change in the DNA sequence that occurs naturally without human intervention. These mutations happen due to errors that can occur during DNA replication, where the DNA polymerase enzyme may insert the wrong nucleotide or slip, resulting in insertion or deletion mutations. This type of mutation is part of the natural processes that contribute to genetic variation within a population.

In contrast, induced mutations result from external factors such as chemicals or radiation that alter DNA. Neutral mutations generally do not affect an organism's fitness, although they can still arise as spontaneous changes. A transversion mutation is a specific type of point mutation where a purine is replaced with a pyrimidine or vice versa, and while this can happen spontaneously, it is not the broad category that describes all natural mutations.