Genome Diversity

Click the Figure for a graphical depiction of the many different types of viral genome found in virions.

DNA						RNA
double-stranded			single-stranded			double-stranded		single-stranded
linear	circular		linear	circular		linear		linear (circular)*
single	single	multiple	single	single	multiple	single	multiple	(+)sense		(-)sense
								single	multiple	single	multiple

* = viroids only

Viruses are the only organisms on this planet to still have RNA as their sole genetic material. They are also the only autonomously replicating organisms to have single-stranded DNA. The range of virus genomes as found in virions encompasses:

single-component dsDNA, linear or circular (occasionally circularly permuted linear);
single, double or multi-component circular ssDNA;
single-component linear ssDNA;
single or multi-component dsRNA;
single or multiple component ssRNA genomes which may be

totally "positive"(or messenger) polarity,
totally "negative" (or anti-messenger) polarity, or
partially positive negative-sense;

"diploid" positive-sense ssRNA genomes which replicate via reverse transcription to and transcription from longer-than-genome-length dsDNA, and
nicked and/or partially dsDNAs which replicate via transcription to and reverse transcription from longer-than-genome-length positive-sense ssRNA.

In contrast, prokaryotes have mainly single-component circular (occasionally multiple) or linear dsDNA (Streptomyces, Helicobacter) while all eukaryotes have multi-component linear dsDNA, and all the genomes replicate via the classic semi-conservative route.

Viral genome types have inspired a classification based on what is found in virions, coupled with their replication strategy. This is the Baltimore Classification, and will be discussed in a broader treatment of Virus Replication.

An overview of the taxa Recognized in the Universal System of Virus Taxonomy in terms of their genome content may be found here.

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