Answer:
Inducible
Step-by-step explanation:
When a gene is expressed only under certain conditions such as the presence of an inducer in the environment to inactivate the repressor, the gene expression is said to be inducible. Here, the presence of substance Y is required as it serves as an inducer by inactivating the repressor protein. When the repressor protein is inactivated, RNA polymerase is able to express the gene. This is an example of inducible gene expression. For example, the presence of lactose is required for the expression of genes of the lac operon.