Q.69 The transfer of DNA from one bacterial strain to another by a virus and the
subsequent recombination between the chromosomes of the recepient cells and the
introduced DNA is called as:
1. Transformation
2. Transduction
3. Conjugation
4. Recombination
Bacterial transduction is a key horizontal gene transfer mechanism in microbiology. The correct answer to Q.69 is 2. Transduction.
Correct Answer
The process described—DNA transfer from one bacterial strain to another by a virus, followed by chromosomal recombination in the recipient—is transduction. A bacteriophage (virus) infects a donor bacterium, packages bacterial DNA into new phage particles, and delivers it to a recipient cell. There, homologous recombination integrates the DNA via host enzymes like RecA.
Transformation Explained
Transformation (Option 1) involves direct uptake of free extracellular DNA from the environment by competent recipient bacteria. No virus or cell contact is needed, but it’s DNase-sensitive as naked DNA degrades easily. Recombination follows uptake, but lacks a viral vector.
Conjugation Explained
Conjugation (Option 3) requires direct cell-to-cell contact via a pilus, transferring plasmid DNA (often with chromosomal genes) from donor to recipient. It’s a sexual process mediated by conjugative plasmids like F-plasmid, without viruses.
Recombination Clarified
Recombination (Option 4) is the general integration of transferred DNA into the recipient chromosome, common to all three mechanisms (transformation, transduction, conjugation). It is not the transfer method itself.
Key Differences Table
| Process | Mechanism | Vector/Agent | Cell Contact | DNase Resistance |
|---|---|---|---|---|
| Transformation | Uptake of free DNA | None (naked DNA) | No | No |
| Transduction | Virus packages DNA | Bacteriophage | No | Yes |
| Conjugation | Pilus-mediated transfer | Conjugative plasmid | Yes | Yes |
| Recombination | DNA integration | Host enzymes (RecA) | N/A | N/A |
Transduction types include generalized (random DNA fragments) and specialized (prophage-adjacent genes). This MCQ tests core molecular biology concepts for exams.
