Mutation changes DNA sequence and can introduce inherited variation.
Key knowledge
A mutation is a change in DNA sequence. It can arise during replication or from other processes that alter DNA. Whether a mutation enters subsequent generations depends on the affected cell lineage and the organism's route of reproduction.
Conditions and scope
Sequence change does not by itself specify a phenotypic effect or a fitness advantage.
In animals with a segregated germ line, germline and somatic mutations have different routes of transmission; this distinction is not a universal reproductive rule.
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A mutation is a change in DNA sequence. It can arise during replication or from other processes that alter DNA. Whether a mutation enters subsequent generations depends on the affected cell lineage and the organism's route of reproduction.
Replication can introduce DNA-sequence changes; it is not the sole mutation source.
End joining can restore continuity of a double-strand-broken DNA molecule without using a long homologous donor template. Processing and ligation can preserve or change sequence at the junction. This differs from homology-directed repair, whose strand invasion uses another DNA molecule as a template.
Polymerase proofreading can remove a wrongly incorporated nucleotide during synthesis. Mismatch repair corrects selected post-replication pairing errors; excision repair removes damaged DNA and uses synthesis and ligation to restore a strand. These are distinct processes that reduce mutation probability without eliminating all errors.
Unrepaired or misrepaired changes can generate heritable variation.
Chromosomal inheritance can change through nondisjunction or rearrangements such as deletion, duplication, inversion and translocation. These changes can alter dosage, gene context or meiotic pairing. A chromosome image can identify some large changes but does not resolve every sequence variant.
Chromosome changes are one class of genetic variation.
Mutation transfers allele copies between states. In a deterministic two-allele population without other frequency-changing forces, forward and backward mutation update the frequency by the surviving copies plus copies converted from the other allele. Positive rates in both directions give an interior equilibrium; mutation creates variation without necessarily producing rapid population change.
Calling mutations random with respect to adaptation means that they do not generally arise because their future effect would benefit the organism. It does not mean every DNA site has an equal mutation probability or that mutation rates cannot change with environment. Natural selection instead changes representation through differences in survival and reproduction; inherited variation and its fitness effects depend on context.
DNA variation generation has different causes and conditions from its subsequent adaptive representation.