Gene expression is the showing (or hiding) of a specific trait. The lac operon controls whether or not it produces the enzyme B-gal to digest lactose. The lac operon has a repressor protein on the operator to block the enzyme from being produced. This makes sure the operon isn’t producing unnecessary B-gal. In the presence of lactose, the repressor protein temporarily leaves the operon and the RNA polymerase begins to produce the B-gal enzyme. The first picture shows the operon. The second picture shows the operon turned off. The third picture shows the operon turned on.