This system classifies viruses into families based on their genome type (DNA, RNA, single-stranded (ss), double-stranded (ds), etc.) and method of replication. Viruses in each category behave similarly.

1. dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses)
2. ssDNA viruses (+ strand or "sense") DNA (e.g. Parvoviruses)
3. dsRNA viruses (e.g. Reoviruses)
4. (+)ssRNA viruses (+ strand or sense) RNA (e.g. Coronaviruses, Picornaviruses, Togaviruses)
5. (−)ssRNA viruses (− strand or antisense) RNA (e.g. Orthomyxoviruses, Rhabdoviruses)
6. ssRNA-RT viruses (+ strand or sense) RNA with DNA intermediate in life-cycle (e.g. Retroviruses)
7. dsDNA-RT viruses DNA with RNA intermediate in life-cycle (e.g. Hepadnaviruses)