The name given to a unit of bacterial chromosome that controls the expression of a specific set of genes is called an operon.

Here's a breakdown:

* Operon: A group of genes that are transcribed together as a single mRNA molecule, controlled by a single promoter and operator.

* Promoter: A DNA sequence where RNA polymerase binds to initiate transcription.

* Operator: A DNA sequence that controls the access of RNA polymerase to the promoter.

The operon concept is a key mechanism for gene regulation in bacteria. It allows for coordinated expression of genes involved in related functions, making it an efficient way to control cellular processes.