Genome Diversity

The range of virus genomes as found in virions includes:

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

* = only viroids, some satellite RNAs and satellite viruses like Hepatitis delta virus (HDV) have circular ssRNA genomes

** = mRNA-sense or translatable. (-)sense is complementary to (+)sense and must be transcribed to give mRNA

Additionally, these genomes may be:

circularly permuted linear single-component dsDNA
single or multiple component (-)ssRNA genomes which may be partially translatable or ambisense;
(+)sense ssRNA genomes replicating via reverse transcription to and transcription from longer-than-genome-length dsDNA, and
dsDNA genomes replicating via transcription to and reverse transcription from longer-than-genome-length positive-sense ssRNA.

Virus genomes range in size from around 1800 nucleotides (ssDNA circoviruses) up to 1.2 million nucleotides (dsDNA, Acanthamoeba polyphaga mimivirus)

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.

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 here in a broader treatment of Virus Replication.

See also the Leicester material here.

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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