The equivalent of a structural gene is: Operon, Recon, Muton, Cistron

Structural genes are the continuous stretch of DNA that regulates a particular genetic trait. A cistron is defined as a unit of function that exhibits cis-trans test and is synonymous with the gene. The smallest unit capable of undergoing recombination is called recon. A cistron has multiple recons and mutons.Therefore, the correct answer is option D.