Viruses, as exceptional entities, can contain either DNA or RNA as heritable genetic material.
Both positive and negative control mechanisms regulate gene expression in bacteria and viruses.
The processes of transcription, mRNA processing and translation are imperfect, and errors can occur and may, in certain cases, alter phenotypes. However, these errors are random, and are not heritable, except in the case of RNA viruses, where the random errors change the genetic information of the virus.
Some viruses are able to transfer genetic information horizontally.
Prokaryotes, viruses and eukaryotes can contain plasmids, which are small extra-chromosomal, double-stranded circular DNA molecules.
Viruses have a unique method of replication that is dependent on the host's metabolic machinery.
Viruses can introduce variation in the host genetic material through lysogenesis or latent infection.
Genetic information in retroviruses is a special case and has an alternate flow of information: from RNA to DNA, made possible by reverse transcriptase, and enzyme that copies the viral RNA genome into the DNA. This DNA integrates into the host genome and becomes transcribed and translated for the assembly of new viral progeny.
Since all organisms, as well as viruses, exist in a dynamic environment, mechanisms that increase genetic variation are vital for a species' ability to adapt to a changing environment.
The basic structure of viruses includes a protein capsid that surrounds and protects the genetic information that can be either DNA or RNA.
Viruses have a mechanism of replication that is dependent on the host metabolic machinery to produce necessary viral components and viral genetic material.
-viruses have highly efficent replicative capabilities that allow for rapid evolution and acquisition of0 new phenotypes.
-viruses replicate via a component assembly model allowing one virus to produce many progeny simultaneously via the lytic cycle
SOme classes of viruses use RNA without a DNA intermediate; however, retroviruses, such as HIV, use a DNA intermediate for replication of their genetic material. Some viruses introduce variation into the host genetic material. When the host is bacterial, it is referred to as lysogenesis; whereas in eukaryotic cells, this is referred to as transformation. Since viruses use the host metabolic pathways, they experience the same potential as the host for genetic variation that results from DNA metabolism.