Question

When lactose operon merodiploids were studied, the analysis that suggested the laco region acts in cis to regulate the lac operon was:____.

a. a nonfunctional laci mutant cannot be rescued by a wild-type laci allele.
b. a nonfunctional laci mutant is rescued by a wild-type laci allele
c. a nonfunctional laco mutant is rescued by a wild-type laco allele
d. a nonfunctional laco mutant cannot be rescued by a wild-type laco allele.
e. none of the answers

Answer 1

The analysis that indicated the lacO region functions in cis as an operator sequence within the lac operon is that a d. nonfunctional lacO mutant cannot be rescued by a wild-type lacO allele.

Step-by-step explanation:

When lac operon merodiploids were studied, the analysis that suggested the lacO region acts in cis to regulate the lac operon was: d. a nonfunctional lacO mutant cannot be rescued by a wild-type lacO allele.

This is because, unlike the lacI gene that produces a diffusible repressor protein which can act in trans, the lacO region is a DNA sequence that functions as an operator and acts in cis.

Thus, if the lacO region on the operon is nonfunctional, even the presence of a wild-type lacO on another DNA molecule would not restore normal regulation, since the operator sequence must be directly in line with the genes it regulates.

In contrast, a nonfunctional lacI gene can be complemented by a wild-type lacI allele present on another DNA molecule within the same cell because the repressor it produces can diffuse within the cell and act on both operons.