The three-domain system divides organisms into groups based on similarities in their:

The three domain system divides organisms into groups based on similarities in their ribosomal RNA. The three domains in the three domain system are the archaea, eukarya and the bacteria. The domains Archaea and bacteria are all prokaryotic microorganisms, or single-celled organisms whose cells have no nucleus. Domain Eukarya on the other hand has organisms whose cells have nucleus.