Question at position 8 Using the nomenclature above, which partial diploid strain will produce β-galactosidase constitutively, and induce expression of permease and transacetylase (A) ?I = Lac repressor genep = the promotero = the operatorZ = the lacZ geneY= the lacY geneA = the lac A geneIsp+ocZ+Y-A-/I-p+o+Z-Y+A+I-p+o+Z+Y-A-/I-p+o+Z-Y+A+I+p-o+Z+Y-A-/I-p+o+Z-Y+A+I+p+ocZ+Y-A-/I+p-o+Z-Y+A+I+p+ocZ+Y-A-/I-p+o+Z-Y+A+Clear my selection

Question

Question at position 8 Using the nomenclature above, which partial diploid strain will produce β-galactosidase constitutively, and induce expression of permease and transacetylase (A) ?I = Lac repressor genep = the promotero = the operatorZ = the lacZ geneY= the lacY geneA = the lac A geneIsp+ocZ+Y-A-/I-p+o+Z-Y+A+I-p+o+Z+Y-A-/I-p+o+Z-Y+A+I+p-o+Z+Y-A-/I-p+o+Z-Y+A+I+p+ocZ+Y-A-/I+p-o+Z-Y+A+I+p+ocZ+Y-A-/I-p+o+Z-Y+A+Clear my selection

BlackTom AI · Accepted Answer

We start by restating the problem to ensure understanding: We are asked, for a partial diploid Lac operon arrangement, which genotype would yield constitutive production of β-galactosidase (Z) while still allowing the permease (Y) and transacetylase (A) to be inducible.
Option 1: I+p+ocZ+Y-A-/I-p+o+Z-Y+A+
- Here, the left plasmid copy contains I+ (no repressor), oc (constitutive operator mutation), Z+ (functional β-galactosidase gene on, constitutive), Y- (permease gene off), A- (transacetylase gene off). The right copy has I- (repressor present), p+ (promoter active), o+ (operator functional), Z- (no β-galactosidase expression), Y+ (permease on), A+ (transacetylase on).
- Implication: Z is constitutive on the left, but Z on the right is repressed, and the overall operon expression is a mix. Permease and transacetylase are on the right but depend on operator regulation and repressor presence. The pattern does not clearly guarantee constitutive Z with inducible Y and A.
Option 2: I-p+o+Z+Y-A-/I-p+o+Z-Y+A+
- Both copies have I- (repressor present) and the same promoter and operator configuration, with Z+ on both sides but Y-A- on the left and Y+A+ on the right. Repression by LacI would prevent substantial Z expression unless allolactose relieves it; since I- indicates an absent repressor, this would more likely lead to constitutive expression only if operator is nonfunctional. Here o+ is functional, so repression may occur, making this unlikely to produce constitutive Z with inducible Y and A.
Option 3: I-sp+ocZ+Y-A-/I-p+o+Z-Y+A+
- This option introduces sp (likely a typo for Isp, possibly indicating a repressor status), with oc on the left, and Z+ Y- A- on the left, and the right side showing Z-Y+A+ with I-p+o+. The mix again does not clearly satisfy constitutive Z while making Y and A inducible, because the repressor status and operon configuration do not consistently align to produce the requested pattern.
Option 4: I-p+ocZ+Y-A-/I-po+Z-Y+A+
- Here we have I-p+ (repressor present or promoter context unclear), oc on the left, Z+ with Y- A-, and on the right p o+ changes in operator status, with Z-Y+A+ on that side. The altered operator and promoter arrangement could disrupt coordinated expression such that Z is not reliably constitutive while Y and A are induced, making this option problematic for the stated phenotype.
Option 5: I+p+ocZ+Y-A-/I-p+o+Z-Y+A+
- This configuration mirrors a pattern where the left copy carries I+ (no repressor), oc (constitutive operator), Z+ (constitutive β-galactosidase), Y- and A- (permease and transacetylase off). The right copy has I+ (no repressor), p+ (promoter active), o+ (operator functional), Z- (no β-galactosidase), Y+A+ (permease and transacetylase on). The combination can yield constitutive Z expression from the left copy via oc, while Y and A can be induced from the right copy when the operator allows transcription and the Z gene on that copy is not blocking the operon’s overall output. This arrangement most closely aligns with the requested phenotype: constitutive Z and inducible Y and A.
Across options, a key misconception is assuming constitutive operator mutations always guarantee a uniform expression pattern across all operon genes or assuming that repressor presence alone dictates the outcome. The correct reasoning hinges on understanding how oc (constitutive operator) can derepress Z while the surrounding regulatory context (I+, I-, promoter status) determines whether Y and A respond to induction. By comparing the left-right copy configurations, option 5 stands out as the one that best supports Z being constitutive due to oc on the left while allowing Y and A to be inducible on the right where the operator and promoter configuration permit their expression under induction.

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