Paper I — 2019 July (Supplementary) (2010 Scheme) — Q6
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Paper I
2019 July (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Enumerate methods of gene – transfer in bacteria
Q62 marksShort Notes
Answer
Methods of gene transfer in bacteria (horizontal gene transfer):
Conjugation — direct cell-to-cell transfer of plasmid DNA (e.g., F plasmid, R plasmid) from a donor to a recipient bacterium via a sex pilus, forming a conjugation bridge through which DNA passes; the principal mechanism spreading multidrug-resistance (R) plasmids between bacteria.
Transduction — transfer of bacterial DNA via a bacteriophage acting as vector; generalized transduction occurs when a lytic phage mistakenly packages random host DNA; specialized transduction occurs when a temperate (lysogenic) phage carries adjacent bacterial genes on excision from its integrated site.
Transformation — direct uptake of free/naked DNA released from lysed bacteria in the environment by a competent recipient bacterial cell, which then incorporates it into its own genome by recombination — the mechanism first demonstrated in Griffith’s classical pneumococcal transformation experiment.
(Also sometimes described) Transposition — movement of transposable genetic elements (“jumping genes”) between plasmids and the chromosome within a cell, which, while not itself a mechanism of transfer between different bacterial cells, contributes to the reassortment/dissemination of resistance genes once they enter a new cell via one of the above mechanisms.
