The equivalent of a structural gene is

Structural genes are genes that have information for the formation of proteins. These are also known as cistrons.
(1) Muton is unit of mutation. It is the smallest element of genetic material capable of undergoing distinct inheritable change. It is usually identified as a single pair of nucleotides.
(3) Operon is an association of structural genes that code for enzymes related to a metabolism or related reactions of different metabolism which, in return, are associated with some regulatory genes and sequences, like promoter, operator etc.
(4) Recon is that portion of genetic material capable of genetic recombination during meiosis due to crossing over. A cistron may contain hundreds of moutons and recons.