in the cytoplasm, in which case they have evolved or acquired their own means of executing transcription and replication. dsDNA viruses are also commonly divided between tailed dsDNA viruses, referring to members of the realm Duplodnaviria, usually the tailed bacteriophages of the order Caudovirales, and tailless or non-tailed dsDNA viruses of the realm Varidnaviria. dsDNA viruses are classified into three of the four realms and include many taxa that are unassigned to a realm: All viruses in Adnaviria are dsDNA viruses. Viruses in this realm infect archaea. All viruses in Duplodnaviria are dsDNA viruses. Viruses in this realm belong to two groups: tailed bacteriophages in Caudovirales and herpesviruses in Herpesvirales. In Monodnaviria, members of the class Papovaviricetes are dsDNA viruses. Viruses in Papovaviricetes constitute two groups: papillomaviruses and polyomaviruses. All viruses in Varidnaviria are dsDNA viruses. Viruses in this realm include adenoviruses, giant viruses, and poxviruses. The following taxa that are unassigned to a realm exclusively contain dsDNA viruses: Classes: Naldaviricetes Families: Ampullaviridae, Bicaudaviridae, Clavaviridae, Fuselloviridae, Globuloviridae, Guttaviridae, Halspiviridae, Ovaliviridae, Plasmaviridae, Polydnaviridae, Portogloboviridae, Thaspiviridae Genera: Dinodnavirus, Rhizidiovirus Group II: single-stranded DNA viruses The second Baltimore group contains viruses that have a single-stranded DNA (ssDNA) genome. ssDNA viruses have the same manner of transcription as dsDNA viruses. Because the genome is single-stranded, however, it is first made into a double-stranded form by a DNA polymerase upon entering a host cell. mRNA is then synthesized from the double-stranded form. The double-stranded form of ssDNA viruses may be produced either directly after entry into a cell or as a consequence of replication of the viral genome. Eukaryotic ssDNA viruses are replicated in the nucleus. Most ssDNA viruses contain circular genomes that are replicated via rolling circle replication (RCR). ssDNA RCR is initiated by an endonuclease that bonds to and cleaves the positive strand, allowing a DNA polymerase to use the negative strand as a template for replication. Replication progresses in a loop around the genome by means of extending the 3′-end of the positive strand, displacing the prior positive strand, and the endonuclease cleaves the positive strand again to create a standalone genome that is ligated into a circular loop. The new ssDNA may be packaged into virions or replicated by a DNA polymerase to form a double-stranded form for transcription or continuation of the replication cycle. Parvoviruses contain linear ssDNA genomes that are replicated via rolling hairpin replication (RHR), which is similar