3. The lac operon is an example of a(n)a) constitutive geneC) repressed geneb) induced gened) two of the above

The lac operon is an example of both an induced gene and a repressed gene.

Here's why:

1. Induced gene: The lac operon is normally switched off, but in the presence of lactose (the inducer), it is switched on. This is because lactose binds to the repressor protein and prevents it from binding to the operator. This allows RNA polymerase to bind to the promoter and transcribe the genes, thus it is an induced gene.

2. Repressed gene: In the absence of lactose, the lac operon is switched off. This is because the repressor protein binds to the operator, preventing RNA polymerase from binding to the promoter and transcribing the genes. Thus, it is also a repressed gene.

So, the answer is d) two of the above.