Answer:
Step-by-step explanation:
The genetic information present in all cells can be compared to a book of blueprints prepared for the construction of a large, multipurpose building.
-At different times, all of the blueprints will be needed, but only a small subset is consulted during the work on a particular floor or room.
-Similarly in the case of cells all the necessary genetic information is present but but only a subset of genes is expressed in any particular cell.
Regulation of gene expression alters the gene function in many ways.
For example in prokaryotes-
The lac operon is an inducible operon, in which the presence of a key metabolic substance which is lactose in this case, initiates transcription of the operon, allowing synthesis of the proteins encoded by the structural genes.
In case of repressor operon: Transcription of the structural genes is controlled by a repressor protein that is synthesized by a regulatory gene, which is also part of the operon. It binds to the operon and blocks the movement of Rna polymerase.