Final answer:
Viral genomes can vary widely in terms of the number and types of genes they contain. They can be composed of RNA or DNA, and may be single or double stranded. Viruses tend to have smaller genomes compared to bacteria or eukaryotes, containing only the genes necessary for replication.
Step-by-step explanation:
Viral genomes show extensive variation and may be composed of either RNA or DNA, and may be either double or single stranded. They can be small compared to bacteria or eukaryotes, containing only the genes necessary for the virus to replicate. The range of genes found in viruses can vary from a few to several hundred, depending on the complexity of the virus.
For example, the X174 virus has nine genes, while the E. Coli genome consists of about 4,400 genes, and the human genome contains about 100,000 different genes.
In some cases, viral genomes may have genes within genes or overlapping genes, where part of one gene will also be part of another gene. This is not commonly observed in cellular genomes.