A DNA virus is a virus that replicates via a DNA-dependent DNA polymerase and has DNA as its genetic material. The Baltimore categorization system divides viruses into two groups: Group I (double-stranded DNA; dsDNA) and Group II (single-stranded DNA; ssDNA). Infected cells normally extend single-stranded DNA to double-stranded DNA. Plants have a low prevalence of DNA viruses. Only lower plants, such as eukaryotic algae, are infected by dsDNA viruses, which account for 17% of all plant viruses. DNA viruses have genomes that are replicated by DNA polymerases encoded by either the host or the virus. DNA viral genomes are highly diverse, and the relative stability of DNA allows for genomes that are far larger than those of RNA viruses. DNA viruses that infect mammals have genomes that range in size from under 2 kb of single-stranded DNA to over 375 kb of double-stranded DNA. Eukaryotic bacteria are infected by much larger DNA viruses.