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Mutations are permanent changes in the DNA sequence of an organism or cell. They can arise in germline cells and be inherited by offspring, or occur in somatic cells and affect only the individual. Most mutations are neutral or near-neutral, having little immediate effect, but some can alter gene function and phenotype.

Mutations vary in type. Point mutations replace a single nucleotide and can be synonymous, missense, or nonsense; insertions and deletions add or remove nucleotides and can cause frameshifts; larger structural changes include duplications, inversions, and chromosomal rearrangements. In organisms with rapid reproduction, such as bacteria, small mutations can spread quickly under selection.

Causes include errors during DNA replication, exposure to mutagens such as chemicals or ultraviolet and ionizing radiation, and mobile genetic elements that transpose within the genome. Some mutations arise as a result of recombination or viral integration.

Mutations drive evolution by providing genetic variation on which natural selection and genetic drift act. They also underlie many diseases when they disrupt essential genes or regulatory regions, including cancer, inherited disorders, and drug resistance. Not all mutations are harmful; some confer advantages in particular environments.

Researchers study mutations using sequencing, comparative genomics, and functional assays. Understanding mutation rates and spectra informs fields from medicine to conservation, and underpins technologies like genome editing and precision medicine. Overall, mutations are a fundamental source of genetic diversity and a central concept in biology.