Practice question

Horizontal gene transfer refers to non-vertical transmission of genetic material between unrelated organisms via transformation, transduction, conjugation or vectors. Agrobacterium tumefaciens exemplifies natural inter-kingdom transfer, possessing Ti plasmid bearing T-DNA flanked by border repeats. Virulence proteins excise T-DNA and deliver it through type IV secretion system into plant nucleus where it integrates, expressing oncogenes inducing crown gall formation. This natural gene delivery system underlies plant transgenesis. Acquisition of novel genes through such mechanisms spreads antibiotic resistance among bacteria and introduces foreign functions outside Mendelian inheritance.