A mutation is an accidental change in an organism's DNA sequence. Mutations can alter a single DNA letter, affect a larger stretch of genetic material, or sometimes involve whole chromosomes.
Mutations arise through errors when DNA is copied, damage caused by radiation or chemicals, or other biological processes. Some occur in body cells and are not passed to offspring; mutations in eggs, sperm, or their precursor cells can be inherited. Their effects range from harmful to beneficial to apparently neutral.
Mutation is not the same as adaptation. A mutation is a genetic change, while an adaptation is an inherited trait that becomes more common because it improves survival or reproduction in a particular environment. Likewise, gene flow moves genes between populations, recombination reshuffles existing genetic variants, and genetic drift changes variant frequencies by chance.