A lack of the repressor would lead to constant, and wasteful, expression of the genes for lactose metabolism. An inability of the inducer (allolactose) to bind to the repressor would have the opposite effect, preventing gene expression for lactose metabolism.
Work Step by Step
To understand this, consider the normal roles of the repressor and the inducer: to stop or to initiate expression of genes for the metabolism of lactose. Removing either of these (see Fig. 16.4) would have the opposite effect compared to normal.