Sometimes in a phage infection cycle, some host DNA is packaged in the phage head during assembly.
When that DNA is injected into the next host cell,
crossing over between the injected DNA and the homologous region of the bacterial chromosome results in
recombination, as in transformation.
Like transformation, transduction can be used to establish "linkage",
since bacterial genes that are close together have a high probability of cotransduction, and
relative mapping distances between linked genes can be determined.