1. 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+
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)
a. +,+ d. -,+
b. -,- e. cannot tell for certain
c. +,-
2. 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 B: I - Oc Z+/ Fʹ I - O+ Z-
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)
a. +,+ d. -,+
b. -,- e. cannot tell for certain
c. +,-
1. 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+
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)
a. +,+ d. -,+
b. -,- e. cannot tell for certain
c. +,-
2. 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 B: I - Oc Z+/ Fʹ I - O+ Z-
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)
a. +,+ d. -,+
b. -,- e. cannot tell for certain
c. +,-
Related textbook solutions
Related questions
1. The lac operon of E. coli controls the expression of genes that code for enzymes involved in lactose metabolism. The operon system is inducible in that it can be âturned onâ by the presence of lactose. Mutations to various regions of the lac operon have been discovered which affect both the control of gene expression and the function of the gene products.
These mutations include:
I - = produces a repressor protein that can not bind to the operator region
I s = produces a repressor protein that can not be removed from the operator region
O C = can not bind a repressor protein
Z - = produces a defective (non-functioning) β-galactosidase enzyme
( I- are recessive to I+; I+ recessive to IS )
Detail the functionality of the lac
operon under the following genetic and cellular conditions.
| GENES | Lactose present | Repressed (yes/no) | Constitutive (yes/no) | Inducible (yes/no) |
| I + O + Z + | no | |||
| I + O C Z + | no | |||
| I S O + Z + | yes | |||
| I - O + Z + | yes | |||
| I S O C Z + | no |
