virus: Classification


Viruses are not usually classified into conventional taxonomic groups but are usually grouped according to such properties as size and shape, the virus's chemical composition and genome, and the method by which the virus reproduces. These features include the type of nucleic acid a virus contains, DNA or RNA, whether the virus is single- or double-stranded, and the structure of the capsid and the number of protein subunits in it. It has been estimated by virologists, based on the number species of living things that viruses might infect, that there could be as many as 200 million viruses, or perhaps many more, but less than 10,000 viruses have been named and classified.

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