Isochor

Isochor is not a standard term with a single, widely accepted definition. In most scholarly contexts, the form isochoric refers to a constant-volume process, and isochores denotes large regions of DNA with uniform base composition. When isochor appears, it is usually a misspelling or shorthand in informal writing.

In thermodynamics, isochoric describes a process at constant volume (V). In such a process, no mechanical work is done by the system on its surroundings because the volume does not change. For an ideal gas, the heat added equals the change in internal energy, Q = ΔU = n Cv ΔT, while pressure changes with temperature according to P = nRT / V. The term isochoric is commonly preferred over isochor in formal discussions of constant-volume processes.

In genomics, isochores are large, megabase-scale regions of the genome with relatively uniform GC content. Isochores are categorized into families by GC level and have been associated with patterns of gene density, replication timing, and chromosomal structure. The standard spelling in this context is isochores; isochor is not used in formal genomic literature.

Usage guidance for writers: use isochoric when describing thermodynamic constant-volume processes, and isochores when referring to the genome architecture feature. The form isochor is uncommon and generally indicates misspelling or non-specialist shorthand. Related terms include isobar (constant pressure) and isochron (equal time), which are distinct concepts in their respective domains.