Dear student
 
In lac operon
i gene - Repressor
z gene - ββ- galactosidase
y gene - Permease
a gene - Transacetylase.
So, the correct answer is '(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)'
						

							
The LacI gene is a regulatory gene that codes for the lactose-inducible lac operon transcriptional repressor. In other words, it codes for the respressor of te Lac-operon. LacI is always transcribed. When the repressor binds to the operator, the Lac genes can't be transcribed.
The lacZ gene encodes an enzyme called β-galactosidase, which is responsible for splitting lactose (a disaccharide) into readily usable glucose and galactose (monosaccharides). The lacY gene encodes a membrane protein called lactose permease, which is a transmembrane "pump" that allows the cell to import lactose.
The operon model of prokaryotic gene regulation was proposed by Fancois Jacob and Jacques Monod. ... The regulator gene codes for a repressor protein that binds to the operator, obstructing the promoter (thus, transcription) of the structural genes. The regulator does not have to be adjacent to other genes in the operon.
cAMP binds to the CRP, decreasing its affinity for a DNA site near the promoter. cAMP binds to the Lac repressor, decreasing its affinity for a DNA site near the promoter. cAMP binds to the Lac repressor, increasing its affinity for a DNA site near the promoter.