Discussion
In specialised transduction, the genes transferred are
Answer: B
Correct answer: only those adjacent to the prophage integration site
In specialised transduction only the host genes adjacent to the prophage integration site can be transferred. The mechanism explains the restriction. A temperate phage integrates at a specific site, and when it excises it occasionally does so imprecisely - cutting a little to one side, so that it leaves some phage DNA behind and carries an equivalent length of neighbouring host DNA away. Only genes physically next to the integration site can be picked up this way. The classic example is phage lambda in E. coli, which integrates between the gal and bio genes and can therefore transduce only those. The contrast with generalised transduction is the point examined. There the phage packages a random fragment of fragmented host DNA during the lytic cycle, so any gene may be carried with roughly equal probability. The resulting particles are usually defective, having exchanged phage genes for host ones.
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