An Hfr strain of Escherichia coli undergoes aberrant excision of the integrated F factor so that the excised plasmid now carries the adjacent lac operon along with F genes. When this F-prime lac plasmid is transferred into an F-minus recipient, the most likely outcome is:
- A The recipient becomes F-positive and a stable partial diploid carrying two copies of lac genes ✓
- B The entire donor chromosome is transferred at high frequency
- C The recipient remains F-minus and receives no lac genes
- D The recipient converts into a new Hfr strain with the F factor integrating at the same original site
Correct answer: A. The recipient becomes F-positive and a stable partial diploid carrying two copies of lac genes
Explanation
This process is called sexduction or F-prime transfer. The recipient acquires the autonomous F-prime plasmid and therefore becomes F-positive and capable of further conjugative donation, while the lac genes carried on the plasmid create a merodiploid state with one chromosomal and one plasmid copy of lac. Full chromosome transfer is a property of Hfr crosses and is not required here, and the recipient need not integrate the plasmid to express the acquired genes.
Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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