Question at position 4 In the genotype presented below, what will the expression phenotype for beta-galactosidase and permease be, respectively.For the genotype (Isp+ocZ+Y-A+/I+p-o+Z-Y+A+)?I = Lac repressor genep = the promotero = the operatorZ = the lacZ geneY= the lacY geneA = the lac A geneconstitutive and absentconstitutive and inductiveabsent and inductiveinductive and absentinductive and constitutive

Question

Question at position 4 In the genotype presented below, what will the expression phenotype for beta-galactosidase and permease be, respectively.For the genotype (Isp+ocZ+Y-A+/I+p-o+Z-Y+A+)?I = Lac repressor genep = the promotero = the operatorZ = the lacZ geneY= the lacY geneA = the lac A geneconstitutive and absentconstitutive and inductiveabsent and inductiveinductive and absentinductive and constitutive

BlackTom AI · Accepted Answer

We are given a diploid lac operon genotype: (Isp+ocZ+Y-A+/I+p-o+Z-Y+A+). Interpreting the symbols:
- I: Lac repressor gene; I+ = functional repressor, Isp = superrepressor variant that cannot be induced.
- p: promoter; p+ = functional promoter, p- = defective promoter.
- o: operator; o+ = normal operator that can be bound by the repressor, oc = constitutive operator mutation that cannot be bound by the repressor.
- Z: lacZ gene (beta-galactosidase);
- Y: lacY gene (permease);
- A: lacA gene (galactosidase acetyltransferase).

Now, parse each chromosome in the genotype:
- On the first chromosome: Isp+ oc Z+ Y- A+.
  - Isp+ (superrepressor active): this repressor is constitutively active and resistant to induction.
  - oc (constitutive operator): the operator is mutated so that repressors cannot bind here, making transcription constitutive on this chromosome regardless of repressor status.
  - Z+ and A+ indicate functional beta-galactosidase and acetyltransferase, and Y- indicates a nonfunctional permease on this chromosome.
- On the second chromosome: I+ p-o+ Z- Y+ A+.
  - I+ (functional repressor): can bind the operator to repress transcription, provided the operator is available.
  - p- (defective promoter): transcription cannot initiate from this chromosome due to a defective promoter.
  - o+ (normal operator): can be bound by I+ to repress transcription on this chromosome when appropriate.
  - Z- and Y+ indicate a nonfunctional beta-galactosidase but functional permease on this chromosome.

Now determine expression of the two enzymes in the cell:
- Beta-galactosidase (Z): On the first chromosome, Z+ means beta-galactosidase is produced. The oc operator mutation makes this expression constitutive, and because the first chromosome’s Z+ is present, it will contribute to beta-galactosidase activity. The second chromosome has Z-, and its promoter is p- so it cannot contribute. Overall, beta-galactosidase is expressed constitutively.
- Permease (Y): The first chromosome has Y- (no permease). The second chromosome has Y+ (permease) but the promoter is p- (defective), so transcription cannot start from that chromosome either. Therefore, permease is not produced.

With this in mind, evaluate each answer choice:
- constitutive and absent: This matches our reasoning — beta-galactosidase is constitutively expressed due to the oc mutation on the first chromosome, while permease is absent because both chromosomes fail to produce Y product (first chromosome Y- and second chromosome p- prevents transcription of Y+).
- constitutive and inductive: Inductive expression would require induction of the operon, which is not relevant here since Z is on a chromosome with oc making it constitutive and the second chromosome cannot contribute due to p-; there is no inductive condition at play that would switch the expression to a higher or different pattern.
- absent and inductive: This would claim beta-galactosidase is not expressed, which is incorrect because Z+ on the first chromosome is constitutively expressed due to oc.
- inductive and absent: Similar issue as above for beta-galactosidase, plus the notion of induction is unnecessary here; the first chromosome overrides with constitutive expression.
- inductive and constitutive: The first enzyme being constitutive is correct, but permease is not constitutively expressed here because both chromosomes fail to produce permease (p- blocks the second chromosome, and Y- on the first chromosome prevents production on that chromosome). Therefore this pairing is inaccurate.

Taken together, the only option that aligns with the genotype’s effective regulation and the resulting phenotypes for the two enzymes is: constitutive and absent.

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When glucose is present, and lactose is absent in the bacteria cell’s environment, which of the following is INCORRECT with respect to the lac operon?

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