Q.42 Lederberg and Tatum describe the phenomena of-
1. Transformation
2. Conjugation
3. Mutation
4. Transversion
Title: Lederberg and Tatum Experiment: Discovery of Bacterial Conjugation Explained
Lederberg and Tatum described bacterial conjugation, a process where genetic material transfers between bacteria via direct cell-to-cell contact.
Correct Answer: 2. Conjugation
In 1946, Joshua Lederberg and Edward Tatum demonstrated conjugation using auxotrophic E. coli strains (one needing biotin, phenylalanine, cysteine; the other threonine, leucine, threonine). When mixed and plated on minimal medium, prototrophic recombinants appeared, proving genetic exchange—not mutation or transformation. This overturned the asexual reproduction dogma for bacteria.
Experiment Overview
They ruled out transformation (no free DNA added) and cross-feeding via controls: separate cultures yielded no prototrophs. Conjugation involves F+ (donor) transferring plasmid DNA via sex pilus to F- (recipient), enabling recombination.
Explanation of All Options
| Option | Description | Relation to Lederberg-Tatum |
|---|---|---|
| 1. Transformation | Uptake of naked DNA from environment (Griffith, 1928; Avery, 1944). | Incorrect: Their experiment used live cells; no exogenous DNA. |
| 2. Conjugation | Direct genetic transfer via cell contact (F-plasmid). | Correct: Their 1946 discovery. |
| 3. Mutation | Spontaneous/permanent DNA change in genome. | Incorrect: Recombinants showed mixed parental traits, not new mutations. |
| 4. Transversion | Purine↔pyrimidine base substitution (e.g., A↔C). | Incorrect: Molecular term; unrelated to their phenotypic mixing experiment. |
