Gene regulation governing lactose operon of E.coli that involves the lac I gene product is
A. Negative and repressible because repressor protein prevents transcription
B. Feedback inhibition because excess of beta- galactosidase can switch off transcription
C. Positive and incusible because it can be induced by lactose
D. Negative and inducible because repressor protein prevents transcription

Hint: There are different ways of gene regulation, like pathways for regulating whether and at what levels of genes are expressed. A lot of gene regulation, however, happens at the transcription level. There are unique regulatory molecules in bacteria that regulate whether a specific gene would be transcribed into mRNA. These molecules also work by binding to DNA near the gene and helping or blocking the RNA polymerase, the transcription enzyme.

Complete answer:
Based genes are mostly located in bacteria in a cluster on the chromosome, where they are transcribed as a single unit from one promoter (RNA polymerase binding site). Such a gene cluster under the guidance of a single promoter is referred to as an operon. Operons are common in bacteria, but in eukaryotes, such as humans, they are uncommon. A regulatory repressor protein is usually bound to the operator in negative inducible operons, which prevents the genes in the operon from being transcribed. If an inducer molecule is present, it attaches and alters its conformation to the repressor such that it does not bind to the operator. This activates the operon 's voice. A negatively regulated inducible operon is the lac operon, where allolactose is the inducer molecule.
Operas aren't just composed of gene coding sequences. Instead, they also have regulatory DNA sequences that regulate the operon's transcription. These sequences are usually binding sites for regulatory proteins that regulate how much transcription of the operon takes place. One example of a regulatory DNA sequence is the promoter, or the site where RNA polymerase binds.

Hence, the correct answer is (D).

Note: Many genes play specific roles and, as mentioned above, are expressed only under certain conditions. There are also genes, however, whose products are continuously required by the cell for vital functions to be retained. Under normal growth conditions, these housekeeping genes are continuously expressed. Promoters and other regulatory DNA sequences have housekeeping genes that ensure steady expression.