Transduction is genetic recombination mediated by phages.

A phage infects a "donor" bacterium.

In its lytic cycle, the phage accidentally packages some "donor" DNA (e.g. A^+ allele) in its protein coat.

When progeny phage then infect a "recipient" cell, DNA from the "recipient" may exchange with that of the "donor".

The "recipient" becomes a recombinant (A^+ B^-).