Bacterial strains that are “partially diploid” have two copies of the lac operon because they aquired a plasmid carrying just the lac operon region.
In this problem you will explore how to solve problems involving partial diploid lac operon bacterial strains.
Bacterial strains that are “partially diploid” have two copies of the lac operon because they aquired a plasmid carrying just the lac operon region. One copy of the lac operon region is on the recipient’s bacterial chromosome, and the other copy is on the P plasmid that was introduced into the cell by conjugation. Partial diploid genotypes are written with the P segment first and the recipient chromosome next.
You create a lac operon partial diploid with this genotype:
F’ I+ P+ Oc Z– Y+ / I– P+ O+ Z+ Y–
To determine which genes are transcribed and under what conditions, you need to first consider each genotype separately, and then together.
Part A
For each region of the lac operon on the P plasmid, I+ P+ Oc Z– Y+, determine whether the region is wild type (that is, it produces a functional protein or it’s a correct protein binding sequence) or whether the region is mutated.
- Select all that apply.
- The promoter sequence is correct/functional.
- The repressor protein is produced.
- The operator sequence is correct/functional.
- Beta-galactosidase is produced from the lacZ gene.
- Permease is produced from the lacY gene.
Part B
Use the information from Part A to determine how the operon is regulated for this genotype (I+ P+ Oc Z– Y+).
- Operon is inducible; permease is produced only in the presence of lactose.
- Operon is repressible; permease is only produced in the absence of lactose.
- Operon is constitutive; permease is produced even when lactose is absent.
- Operon is noninducible; permease is never produced, even when lactose is present.
