Answer :
b. In the presence of the lacl gene product, synthesis of genes in the lac operon were prevented suggested that the lacl gene product must be a repressor.
This evidence suggested that the lacI gene product must be a repressor because when the lacI repressor protein binds to the operator region of the lac operon, it blocks the binding of RNA polymerase to the promoter.
This effectively prevents the transcription of the operon's genes, thereby halting the synthesis of the proteins necessary for lactose metabolism in the absence of an inducer like lactose or allolactose.
