In general, the organization of genes in bacteria is different from that in eukaryotes. In E. coli, approximately 27 percent of all genes are organized into contiguous, functionally related units containing multiple genes under coordinate control that are transcribed as a single unit. Such contiguous gene families are called:.

Explanation:

1. Operon: is a set of genes which are transcribed under the control of an operator gene. These genes are transcribed according to the requirement in the cell under a regulatory mechanism.

2. Or, an operon is a segment of DNA containing adjacent genes including i) structural genes, ii) an operator gene, and iii) a regulatory gene, which are transcribed together.  

3. Thus an operon is a functional unit of transcription and genetic regulation which is regulated in a strict manner.

4. Example of operon; i) Lac operon in E.coli.