In bacterial conjugation, what is the direction of DNA transfer during an F+ × F− mating?

Introduction / Context:Bacterial conjugation is a plasmid-mediated process of horizontal gene transfer. Cells carrying the fertility factor (F plasmid; F+) can form a conjugation pilus and transfer DNA to recipient cells lacking the factor (F−). This concept underlies rapid spread of traits such as antibiotic resistance.

Given Data / Assumptions:

• Donor cell: F+ (encodes pilus, nicking/transfer machinery).
• Recipient cell: F− (lacks F factor).
• Transfer substrate: a single-stranded copy of the F plasmid (or chromosomal DNA if Hfr).

Concept / Approach:Conjugation initiates at the origin of transfer (oriT) on the plasmid in the F+ donor. A relaxase nicks DNA and pilots a single strand through the mating channel into the F− cell. Complementary strands are resynthesized in both cells, converting the recipient to F+ under standard F-plasmid transfer.

Step-by-Step Solution:Identify which cell encodes the conjugative apparatus: F+.Determine directionality: DNA moves donor (F+) → recipient (F−).Conclude that option indicating F+ → F− is correct.

Verification / Alternative check:Hfr strains integrate F into the chromosome and transfer chromosomal segments into F− recipients; direction remains donor to recipient.

Why Other Options Are Wrong:

• F− → F+: recipients cannot initiate transfer.
• “No transfer” options contradict the established mechanism.
• Bidirectional transfer does not occur in classical conjugation.

Common Pitfalls:Confusing transformation, transduction, and conjugation; only conjugation uses the pilus-mediated direct cell–cell bridge.

Final Answer:From F+ cells to F− cells