Q.15

The first evidence of ‘gene transfer’ was demonstrated in 1928 by

(A) Joshua Lederberg in Escherichia coli

(B) Frederick Griffith in Streptococcus pneumoniae

(C) Joshua Lederberg in bacteriophages

(D) Alexander Fleming in Penicillium notetum

First Evidence of Gene Transfer: Griffith’s 1928 Experiment Explained

Frederick Griffith demonstrated the first evidence of gene transfer in 1928 using Streptococcus pneumoniae, marking a pivotal moment in molecular biology. This discovery, known as bacterial transformation, showed genetic material could transfer between bacteria.

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Correct Answer

(B) Frederick Griffith in Streptococcus pneumoniae
Griffith’s experiment involved mixing heat-killed virulent (smooth, S-strain) Streptococcus pneumoniae with live non-virulent (rough, R-strain) bacteria, which then acquired virulence traits from the dead cells. This “transforming principle” was later identified as DNA, providing the earliest proof of horizontal gene transfer in bacteria.

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Option Analysis

(A) Joshua Lederberg in Escherichia coli

Joshua Lederberg discovered conjugation, a different gene transfer mechanism, in E. coli in 1952 with Edward Tatum, involving direct cell-to-cell DNA transfer via plasmids. This occurred decades after Griffith’s work and does not represent the first evidence.

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(B) Frederick Griffith in Streptococcus pneumoniae

Correct, as detailed above. In 1928, Griffith observed live R-strain bacteria transforming into virulent S-strains after exposure to heat-killed S-strains in mice, proving gene transfer without cell division.

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(C) Joshua Lederberg in bacteriophages

Lederberg worked on bacterial genetics but not the first gene transfer via bacteriophages; phage-mediated transduction was later shown by others like Norton Zinder in 1952. No 1928 connection exists here.

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(D) Alexander Fleming in Penicillium notatum

Fleming discovered penicillin from Penicillium notatum in 1928, revolutionizing antibiotics, but this involved fungal antimicrobial production, not gene transfer or bacteria.

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