Question

Bacteria which are stable partial diploids (F’) for the lac operon are grown in the presence or absence of lactose, as indicated below.   The presence (+) or absence (-) of β-galactosidase and permease expression are investigated in these cultures. Which of the following options (A-E) would be the expected results for bacteria with the genotype    I^S P⁺ O⁺ Z⁺ Y^- / I⁺ P⁺ O^C Z^– Y⁺ ?

	β-galactosidase		Permease
	No lactose	Lactose	No lactose	Lactose
A	-	+	-	+
B	-	+	+	+
C	-	-	-	-
D	+	+	-	+
E	-	-	+	+

Question 1 options:

	A
	B
	C
	D
	E

Which one of the following mutations is cis-acting?

Question 2 options:

	TrpR
	I-
	IS
	P-

Answer 1

1) E is right

IS p+ O+ Z+ Y-

I+P+OCZ-Y+

IS stand for super repressor, so in presence of IS there will be no formation of beta galactosidase either in presence or absence of lactose. As Z is absent from second copy.

Oc stand for constitutive operator, it will stimulate expression of its operon Gene's Y in absence or presence of lactose. Because this is a constitutive operator. It does not bind to repressor.

So option E is correct.

2) p- is cis acting element.

Any gene which affect the transcription of near by gene is known cis acting element. Mutation in P lead to inability of binding of RNA polymerase thus decreased transcription of gene.