A replicon is a region of DNA or RNA, sometimes the entire molecule, which replicates from a single origin of replication.

Prokaryotic chromosomes, with the exception of some archaean chromosomes, usually act as a single replicon. Plasmids and bacteriophages are also single replicons, although larger plasmids in some species of bacteria have been found to have more than one replicon.

Eukaryotic chromosomes invariably have multiple replicons per chromosome.