In contrast, the phage vectors are directly tested on an appropriate bacterial lawn (a continuous bacterial growth on an agar plate) where each phage particle forms a plaque (a clear bacteria-free zone in the bacterial lawn). Phage vectors present two advantages over plasmid vectors.
(1) They are more efficient than plasmids for cloning of large DNA fragments; the largest cloned insert size in a λ vector is just over 24 kb, while that for plasmid vectors it is less than 15 kb. In addition,
(2) it is easier to screen a large number of phage plaques than bacterial colonies for the identification of recombinant plaques/clones.
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