The following shows the genotype of a partial diploid bacterial cell - where one
ID: 210013 • Letter: T
Question
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 + or a - whether -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+/ F 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) +,+
B) -,-
C) +,-
D) -,+
E) cannot tell for certain
Explanation / Answer
As the repressor protein can act in both cis and transmodes, it regulartes the gene expresson of both DNA fragement. Due to presence of one functional repressor gene, they both work as a same unit.
in the absence of lactose, the gene cannot expressed because the functional repressor binds to operator.
The answer is "-"
in the presence of lactose, the gene will be expressed because the functional repressor binds to lactose.
The answer is "+"
The answer is D) -,+