Which of the following defines "mutation"?

A mutation specifically refers to a change in the DNA sequence of an organism. This alteration can occur in various ways, such as substitutions, deletions, insertions, or duplications of nucleotide bases. Mutations can arise due to several factors, including errors during DNA replication, exposure to certain chemicals, or radiation. They play a critical role in evolution and genetic diversity, as mutations may affect the traits of organisms and how they adapt to their environment.

In contrast, changes in environmental conditions affect organisms but do not alter their DNA sequences directly. The combination of different traits refers to the phenotypic expression or genetic recombination resulting from sexual reproduction but does not define a mutation. The process of natural selection is a mechanism by which certain traits become more or less common in a population over time, often influenced by mutations, but again, it is not a definition of mutation itself.