Based on rRNA gene sequences, organisms are divided into 3 domains: Bacteria, Archaea, and Eukarya.
Eukarya and Archaea share a common ancestor, and are more closely related to each other than to Bacteria.
Note:
Archaea
and Bacteria
are "prokaryotes" that lack organelles such as a nucleus.
The lack of organelles is not a shared derived character, thus "prokaryotes" do not constitute a monophyletic clade.