Will β-galactosidase be produced under the circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose?

Posted on 2016-10-21 18:48:00 in Biology by ALEXANDRA

The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/). The possible answers indicate with a ʺ+ʺ or a ʺ-ʺ whether β-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.) 

Genotype A: I + O+ Z+/ Fʹ I - O+ Z+ 
Genotype B: I - Oc Z+/ Fʹ I - O+ Z- 
Genotype C: Is Oc Z+/ Fʹ I + O+ Z+ 
Genotype D: I- O+ Z+/ Fʹ I- O+ Z+ 
Genotype E: I + O+ Z+/ Fʹ I + O+ Z+ 
Genotype F: I- Oc Z-/ Fʹ I- Oc Z- 
Genotype G: I- Oc Z+/ Fʹ I- O+ Z+ 
Genotype H: Is Oc Z-/ Fʹ Is O+ Z+ 

Possible Answers: 
a.) (+,+) 
b.) (- , -) 
c.) (+, -) 
d.) (-, +) 
e.) Cannot Tell 

KEY: 
I+ = wild-type repressor 
I- = mutant repressor (unable to bind to the operator) 
Is = mutant repressor (insensitive to lactose) 
O+ = wild-type operator 
Oc = constitutive operator (insensitive to repressor)

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