The lac operon in e. coli consists of genes that code for enzymes necessary for the breakdown of lactose. when lactose is absent, the operon is inactive because a repressor protein binds to a specific site in the lac operon. when lactose is present, lactose molecules bind to the repressor protein, causing the repressor protein to dissociate from the binding site. in the absence of glucose (a preferred energy source for bacteria), the protein cap binds to a regulatory site near the lac promoter to activate transcription of the lac operon.

A summary on Lac Operon

The lac operon in E. coli contains genes that code for enzymes necessary for the breakdown of lactose. It is expressed only in the absence of glucose is but when lactose is present . It has two regulators turn the operon "on" and "off" in response to the corresponding lactose and glucose levels: they are the lac repressor and catabolite activator protein (CAP).

Explanation:

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).