Bacteriophage genetics Which bacteriophage characteristically packages and carries a small piece of the Escherichia coli genome with it (i.e., forms hybrid phage–host DNA particles)?

Introduction / Context:
Different bacteriophages move host genes in distinct ways. Some perform generalized transduction, others specialized transduction, and a few—such as phage Mu—are transposable phages whose life cycles inherently fuse host and phage DNA. Recognizing which phage routinely carries host DNA is vital in microbial genetics and mutagenesis studies.

Given Data / Assumptions:

• We compare λ, Mu, T4, T3, and P1.
• We are looking for a phage that characteristically includes host chromosomal DNA in packaged particles.
• Focus is on the typical outcome, not rare aberrant events.

Concept / Approach:

Phage Mu replicates via transposition, inserting into the host genome randomly. Packaging then frequently captures adjacent host sequences, producing hybrid particles. By contrast, λ performs specialized transduction only after imprecise excision from its specific prophage site, and generalized transducers (e.g., P1, P22) package host DNA stochastically rather than always carrying a host fragment.

Step-by-Step Solution:

Verification / Alternative check:

Genetics manuals describe Mu-driven insertional mutagenesis and frequent host DNA coinheritance within Mu particles, consistent with this answer; λ requires rare faulty excision, and P1 generalizes but does not inherently ensure a host piece per particle.

Why Other Options Are Wrong:

• Lambda (λ): Specialized transduction after rare imprecise excision; not characteristically “always.”
• T4/T3: Typically lytic phages; not used for routine host DNA carriage.
• P1: Generalized transduction but does not inherently package a host fragment each time.

Common Pitfalls:

• Equating “can transduce” with “always carries host DNA.” Terminology matters.
• Confusing specialized (λ) with Mu’s transposable lifestyle.

Final Answer:

Mu (transposable phage)