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A virus has either a DNA or an RNA genome and is called a DNA virus or an RNA virus, respectively. The vast majority of viruses have RNA genomes. Plant viruses tend to have single-stranded RNA genomes and bacteriophages tend to have double-stranded DNA genomes.
RNA viruses are very common. An RNA virus (also known as ribovirus) uses RNA, rather than DNA, for its genetic material. RNA viruses have comparatively high mutation rates. These viruses can be either single or double strands of RNA. The RNA viruses make up four of the six classes of viruses.