Where does variant collide?

Paul Maas's Textkritik (1927, translated as Textual Criticism in 1958) gave the modern statement of the practice: where surviving copies of a text disagree, each differing reading preserved in a particular manuscript witness is a variant, and the editor lists the competing readings in an apparatus below the text. M. L. West's 1973 Textual Criticism and Editorial Technique set out how to collate the witnesses and weigh which variant is likely closest to what the author wrote. Here a variant is a competing version of the words of a text as carried by a physical copy, not an alternative branch inside a data structure or an altered position in a genome.[1][2]

Unit

One differing reading of a passage, attested in a particular witness

Recovery means

Not applicable

Measured by

Recorded by collating manuscript witnesses and listing their disagreements in a critical apparatus

Niklaus Wirth's 1971 The programming language Pascal introduced the variant record: a record type that keeps a common part but can take one of several alternative layouts, chosen by a tag field that says which layout is in use. It extended the record concept from C. A. R. Hoare's earlier work so that a single type could hold a value that is one of several distinct shapes, what is now called a tagged union. Here a variant is a branch within a data structure selected while a program runs, not a competing reading in a manuscript or an alternative form of a DNA sequence.[3]

Unit

One alternative layout of a record, selected by its tag value

Recovery means

Not applicable

Measured by

Fixed in the type declaration by the tag field and its case branches, and checked by the compiler

den Dunnen and Antonarakis's 2000 Mutation nomenclature extensions proposed variant as the neutral term for any place where a DNA sequence differs from a reference, setting it apart from the loaded words mutation and polymorphism. The 1000 Genomes Project Consortium's 2015 A global reference for human genetic variation then catalogued millions of such variants across human populations. Here a variant is an alternative form of a DNA sequence carried at a location in the genome, described by its position and its change, not a reading in a text or a branch in a data structure.[4][5]

Unit

One alternative form of a DNA sequence at a location, given by position and change

Recovery means

Not applicable

Measured by

Detected by sequencing and reported against a reference genome using standard nomenclature