Question

For this question, we focus on four parts:

I, the gene that produces the repressor protein;

P, the promoter region where RNA polymerase binds to initiate transcription;

O, the Operator site, where the repressor binds. When the repressor binds, it prevents transcription; and

ZYA, the three structural genes, all of which are required for the successful utilization of lactose as a food source.

In the left column of the table below, we indicate the genetic composition at the lac operon of particular strains of E. coli cells. A "+" (plus sign) following the letter indicates the wild-type allele (or normally functioning version of the gene). For I, P, and ZYA, a "-" (negative sign) following the letter indicates the mutant allele (or non-functional version of the gene). For the O allele, a "C" indicates the mutant or constitutive allele. It is not functional in that the repressor cannot bind, but it is functional in that transcription can still occur.

Given the conditions stated in each column, please indicate for each genotype whether lac mRNA is produced and at what level by typing in one of the following words in each cell in the table:

"Abundant"

"Minimal"

"None"

The completely wild-type genotype (first row) has already been filled in for you.

	Cellular conditions:
Genotype	Glucose present (low cAMP) and no lactose	Glucose present (low cAMP) and lactose present	No glucose (high cAMP) and lactose present
I+ P+ O+ ZYA+	None	Minimal	Abundant
I- P+ O+ ZYA+
I+ P- O+ ZYA+
I+ P+ Oc ZYA+
I+ P+ O+ ZYA-

Answer 1

Genotype	Glucose present and lactose absent	Glucose and lactose present	No glucose and lactose present
I+ P+ O+ ZYA+	None	Minimal	Abundant
I- P+ O+ ZYA+	Minimal (Inhibitor is inactive)	Minimal (Inhibitor is inactive)	Abundant
I+ P- O+ ZYA+	None (Promoter is inactive)	None  (Promoter is inactive)	None  (Promoter is inactive)
I+ P+ Oc ZYA+	Minimal	Minimal	Abundant
I+ P+ O+ ZYA-	None  (structural gene is inactive)	None  (structural gene is inactive)	None  (structural gene is inactive)