An Escherichia coli strain lysogenised with lambda bacteriophage undergoes induction of the prophage. Rare progeny virions are produced that carry the gal gene located immediately adjacent to the phage attachment site, and these virions transfer the gal gene to a new recipient at high frequency while all other chromosomal genes remain untransferred. This pattern of gene transfer is best explained by:

• A Specialised transduction due to faulty excision of the integrated prophage ✓
• B Generalised transduction due to random packaging of host DNA
• C Conjugation mediated by an integrated fertility factor
• D Transformation by free DNA released from lysed cells

Explanation

When the lambda prophage is induced, imprecise excision occasionally removes a small piece of adjacent bacterial DNA (gal or bio locus) while leaving behind some phage DNA. The resulting defective transducing particle can carry only genes next to the integration site, never the whole chromosome. Generalised transduction is excluded because P22-like or T4-like fully lytic phages package any host fragment randomly, whereas lambda packages only DNA adjacent to att site.

Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.