The correct answer is (1) F. Griffith. He discovered bacterial transformation in 1928 through his pivotal experiment with Streptococcus pneumoniae, demonstrating genetic material transfer between microbes.

Option Analysis

(1) F. Griffith (Correct)

Frederick Griffith observed transformation when heat-killed virulent (smooth, S-type) pneumococci mixed with live non-virulent (rough, R-type) bacteria transformed the latter into virulent forms, killing mice. This revealed a “transforming principle” (later identified as DNA) enabling recombination via DNA uptake.

(2) J. Lederberg

Joshua Lederberg co-discovered conjugation (1946), a DNA transfer mechanism via direct cell contact using E. coli auxotrophs. This is distinct from transformation, which is free DNA uptake without contact.​

(3) E. Tatum

Edward Tatum, with Lederberg, studied conjugation and biochemical genetics in Neurospora, showing gene-enzyme relationships. He did not discover transformation.​

(4) W. Hayes

William Hayes advanced conjugation research, identifying sex factors (F plasmid) in bacteria. His work post-dates and differs from Griffith’s transformation discovery.​

Bacterial transformation discovery by F. Griffith revolutionized genetics. In 1928, this phenomenon—responsible for recombination in microbes—showed DNA as the transforming agent in Streptococcus pneumoniae.

Griffith’s Experiment Explained

Griffith injected mice with live R-strain (non-virulent), heat-killed S-strain (virulent), or both. Only the mixture killed mice, yielding live S-strain bacteria from R-strain—proving stable genetic transformation.

Key Milestones Post-Griffith

Avery et al. (1944) confirmed DNA as the principle. Lederberg/Tatum (conjugation) and others revealed multiple recombination paths: transformation (free DNA), conjugation (contact), transduction (phage-mediated).

Exam Confusions Clarified

• J. Lederberg/E. Tatum: Conjugation pioneers, not transformation.​

• W. Hayes: Elucidated F-plasmid in conjugation.​

Vital for molecular biology MCQs.

Modern Relevance

Transformation enables cloning, gene therapy, and biotech. Griffith’s work paved the way for DNA as genetic material.