A partial diploid containing a wild type allele for lacI and a lacI mutant that was unable to bind the inducer would:
A) always show low levels of β-galactosidase gene expression.
B) show normal induction in the presence of an inducer.
C) express β-galactosidase at all times.
D) only show normal induction in the presence of an inducer in the absence of glucose.
E) show induction in the presence of an inducer in the presence of glucose.

Question

Quizplus · Accepted Answer

The lacI mutant allele that cannot bind the inducer would be dominant in this partial diploid, as the repressor produced by this allele would still be able to bind and repress the lac operon, preventing the induction of β-galactosidase expression. Thus, the system would always show low levels of β-galactosidase gene expression, regardless of the presence of an inducer, because the functional wild type lacI product cannot negate the effect of the mutant repressor on the operon.

A Partial Diploid Containing a Wild Type Allele for LacI