Bacteriophage Evolution
Bacteriophages occur in over 140 bacterial or archaeal genera. They arose repeatedly in different hosts and there are at least 11 separate lines of descent. Over 5100 bacteriophages have been examined in the electron microscope since 1959. Of these at least 4950 phages (96%) have tails. Of the tailed phages 61% have long, noncontractile tails (Siphoviridae). Tailed phages appear to be monophyletic and are the oldest known virus group.
All of the known temperate phages employ one of only three different systems for their lysogenic cycle: lambda-like integration/excision, Mu-like transposition or the plasmid-like partitioning of phage N15.
Read more about this topic: DNA Virus
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