Viral Evolution, Morphology, and Classification

Viruses are infectious particles about 100 times smaller than bacteria and can only be observed by electron microscopy.

The evolution of viruses is speculative as they do not fossilize; biochemical and genetic information is used to create virus histories.

Viruses of all shapes and sizes consist of a nucleic acid core, an outer protein coating or capsid, and sometimes an outer envelope.

Viruses are classified by factors such as their core content, capsid structure, presence of outer envelope, and how mRNA is produced.