Extent and evolution of gene duplication in DNA viruses.

Gene duplication is the main source of genomic novelties and complexities for both eukaryotes and prokaryotes. In contrast, gene duplication appears to be infrequent in the RNA viruses. However, the extent and evolution of gene duplication in DNA viruses remains obscure. Here we perform a genome-wide analysis of gene duplication in the genomes of 250 DNA viruses that represent all known DNA viral genera. While no gene duplication event is identified in single stranded DNA (ssDNA) or reverse transcribing DNA viruses, gene duplication is frequent among double stranded DNA (dsDNA) viruses. For dsDNA viruses, the number of duplicate genes is significantly correlated with the genome complexity. We find that most of duplicate genes experienced purifying selection on average. Our results indicate that gene duplication play an important role in shaping the evolution of dsDNA viruses.