Question

or each of the E. coli strains containing the lac operon alleles listed, indicate whether beta-galactosidase and permease will be synthesized or not (type yes or no)

Genotype	Beta-galactosidase		Permease
	Lactose present	Lactose absent	Lactose present	Lactose absent
I+ P+ O+ Z- Y+ / I+ P+ Oc Z+ Y+
I+ P+ O+ Z+ Y+ / I- P+ O+ Z+ Y-
I- P- O+ Z+ Y- / I+ P+ Oc Z- Y+
Is P+ O+ Z+ Y+ / I- P+ O+ Z+ Y-

Answer 1

Ans:

Genotype	Beta-galactosidase	Permease
Lactose present	Lactose absent	Lactose present	Lactose absent
I+ P+ O+ Z- Y+ / I+ P+ Oc Z+ Y+	Yes	Yes	Yes	Yes
I+ P+ O+ Z+ Y+ / I- P+ O+ Z+ Y-	Yes	No	Yes	No
I- P- O+ Z+ Y- / I+ P+ Oc Z- Y+	No	No	Yes	Yes
Is P+ O+ Z+ Y+ / I- P+ O+ Z+ Y-	No	No	No	No

Explanation: In first partial merozygotes, functional repressor protein (lacI+) unable binds the non functional operator (lacOc). So, the merozygotes produce both beta-galactosidase and permease in the presence or absence of lactose because functional beta-galactosidase (lacZ+) and permease (lacY+) genes are present with functional promoter (lacP+) and nonfunctional operator.

In second partial merozygotes, functional repressor protein (lacI+) binds to the functional operator (lacO+) in both the haploid because lacI+ is trans-acting. So, the merozygotes does not produce beta-galactosidase and permease in the absence of lactose but produces in the presence of lactose with functional beta-galactosidase (lacZ+), permease (lacY+) promoter (lacP+) genes because the inducer lactose binds to repressor protein.

In third partial merozygotes, functional repressor protein (lacI+) unable to binds to the nonfunctional operator (lacOc) in the 2nd haploid. So, the merozygotes produces permease in the absence and presence of lactose (presence of functional lacY+) but does not produces beta-galactosidase both in the presence and absence of lactose because promoter (lacP-) is non functional (RNA polymerase unable to binds) in 1st haploid where functional beta-galactosidase gene is present and nonfunctional beta-galactosidase gene (lacZ-) is present in 2nd haploid.

In fourth partial merozygotes, the trans-acting super-repressor (lacIs) is present that can binds to both functional operator (lacO+). So, the merozygotes does not produces beta-galactosidase and permease in the absence and presence of lactose because the super repressor cannot binds to inducer lactose in the presence of lactose.