Where does locus collide?

In classical rhetoric a locus is a commonplace, a general seat or line of argument that a speaker draws on to find something to say about a case. Aristotle's Topics (ca. 350 BCE) set out these argument places, which he called topoi, and his Rhetoric applied them to persuasion; Cicero's Topica (44 BCE) rendered the idea into Latin as loci, the word this meaning still carries. Ernst Curtius later traced the long life of the locus communis through European literature. Here the word names a reusable pattern of argument in the art of speaking, not a collection of points in geometry or a position on a chromosome.[1][2][3]

Unit

One argument place or commonplace available to a speaker

Recovery means

Not applicable

Measured by

Identified by rhetorical analysis of a text and catalogued in handbooks of topics and commonplaces

In geometry a locus is the set of all points that satisfy a stated condition, so that a curve is described by the property its points share: a circle, for example, is the locus of points at a fixed distance from a centre. Euclid's Elements (ca. 300 BCE) builds the circle from that equidistance property, and Apollonius of Perga's Conics (ca. 200 BCE) treats the conic sections as loci and studies the classical locus problems. Thomas Heath's history documents how these problems ran through Greek mathematics. Here the word names a collection of points fixed by a rule, not a line of argument in speech or a position on a chromosome.[4][5][6]

Unit

One point set, the collection of all points meeting the given condition

Recovery means

Not applicable

Measured by

Given by an equation or a construction whose solutions are exactly the points of the locus

In genetics a locus is the fixed position that a gene or marker occupies on a chromosome, the address at which its variant forms are found. Sturtevant's 1913 map The linear arrangement of six sex-linked factors in Drosophila placed genes in a fixed linear order at measured distances, the first demonstration of such positions, and Morgan, Sturtevant, Muller, and Bridges's 1915 The Mechanism of Mendelian Heredity set the chromosome theory that made the locus a standard unit. Here the word names a place on a molecule of heredity, mapped and counted along a chromosome, not a set of points in geometry or a commonplace in rhetoric.[7][8]

Unit

One chromosomal position, occupied by a gene or marker

Recovery means

Not applicable

Measured by

Mapped by recombination frequency in genetic linkage and by base position in a sequenced genome