Where does mutation collide?

A heritable change in an organism's genetic material, from a single base substitution (a point mutation) to a larger rearrangement, passed on to daughter cells or offspring. Working before the structure of DNA was known, Muller showed in 1927 that X-rays raise the rate of such changes in Drosophila, establishing mutation as a physical event in the gene that could be induced and counted rather than only inferred. The referent is a lineage of cells or organisms, and the unit is an alteration in the DNA sequence itself; what makes something a mutation here is that the sequence changed and the change is transmissible. This is the only meaning on the page where the thing that mutates is a physical molecule and the change is as often unwanted as not.[1]

Unit

An alteration in the DNA sequence, transmissible to offspring

Recovery means

Not applicable

Measured by

Sequencing, or mutation-rate assays that count altered offspring or colonies

A fault introduced into a program on purpose, a mutant, seeded to test whether a test suite would notice it. DeMillo, Lipton, and Sayward proposed mutation testing in 1978: make many small altered copies of a program, each with one changed operator or constant, then run the existing tests. A suite that fails on a mutant has killed it, and the fraction of mutants killed is a mutation score that grades the tests, not the program. The referent is a test suite and the unit is one injected fault; the change is introduced deliberately and is meant to be caught, the reverse of the genetics meaning, where the change is a fact of nature to be detected after it has happened.[2]

Unit

One deliberately injected fault in a program

Recovery means

Not applicable

Measured by

Mutation score: the fraction of injected mutants a test suite detects

A random perturbation applied to a candidate solution inside a genetic algorithm, flipping a bit or nudging a value so the search can reach regions that crossover alone would miss. Holland's 1975 account of adaptation in natural and artificial systems treats mutation as one of the operators acting on a population of encoded solutions, a low-probability source of new variation that keeps the search from converging too early. The referent is a point in a search space and the unit is a change to its encoding; the change is neither a molecular event nor a seeded defect but a tunable knob whose only job is to widen exploration. It borrows the biological word by analogy and keeps almost none of the biology.[3]

Unit

A random change to a candidate solution's encoding

Recovery means

Not applicable

Measured by

A mutation rate, the probability per gene or bit, set as an algorithm parameter

A rule-governed change to the initial consonant of a word, triggered by the grammatical or phonological context around it rather than by any change in the word's meaning. In the Celtic languages, and Welsh especially, a word's first sound shifts across a fixed set of alternations (soft, nasal, and aspirate mutation) depending on what precedes it, so the same lexical item surfaces with different opening consonants. Ball and Müller's account of mutation in Welsh treats this as a morphophonological system rather than a historical accident. The referent is a word form in context and the unit is an alternation at the word's edge; nothing is damaged, injected, or inherited, which sets it apart from every other meaning here.[4]

Unit

An alternation of a word's initial consonant in context

Recovery means

Not applicable

Measured by

Recorded in grammars as mutation paradigms; observed in speech and text