Where does chiasmus collide?

In rhetoric, chiasmus is the figure in which the terms of a first phrase are repeated in reverse order in a second, giving an ABBA pattern, as in "ask not what your country can do for you; ask what you can do for your country." Lanham's A Handlist of Rhetorical Terms and Corbett and Connors' Classical Rhetoric for the Modern Student treat it as a figure of inverted parallelism, named for the Greek letter chi (X) whose two strokes cross. The referent is a pattern of word order on the page, and the name itself is a relatively modern coinage for a crossing figure the ancients already practised. (Our reading, not a claim from these sources: the biology meanings below were named by deliberate analogy to that same crossing image, but they denote entirely different things, which is what makes the shared word a trap rather than a lineage.)[1][2]

Unit

The reversed ABBA ordering of paired terms across two clauses

Recovery means

Not applicable

Measured by

Identified by matching the sequence of terms in the first member against their reversed sequence in the second

In genetics a chiasma (plural chiasmata) is the visible point, seen under the microscope during meiosis, where two homologous chromatids cross over one another and exchange segments, physically marking a recombination event. Jones and Franklin's Meiotic crossing-over: Obligation and interference treats the chiasma as the cytological manifestation of crossover and discusses why at least one forms per chromosome pair and why extra ones are spaced apart. The referent is a crossing of chromosome arms during cell division, again named after the Greek chi, and distinct from both the rhetorical figure and the optic structure.[3]

Unit

The crossover point between homologous chromatids in meiosis

Recovery means

Not applicable

Measured by

Counted cytologically as chiasmata per bivalent and inferred genetically from recombination frequency