The correct option is D Recon
Replicon is the unit of DNA that carries a replication origin site and a termination site and is able of self-replication. A cistron is defined as the unit of function that exhibits cis-trans test. A gene carries several cistrons. The smallest unit capable of undergoing recombination is called as recon. A recon consists of one to several mutants, which are the smallest unit of mutation. Thus, the correct answer is option D.