Which domain is more closely related to Eukarya?

• A. Archaea
• B. Bacteria
• C. Eukarya
• D. Protista

Answer: (A)

Archaea is the domain most closely related to Eukarya. Molecular phylogenies based on ribosomal RNA and many conserved genes show that Eukarya and Archaea share a more recent common ancestor with each other than either does with Bacteria. They also converge on similar features in their core cellular machinery, such as transcription and translation components and DNA packaging proteins (for example, archaeal-like histones and certain RNA polymerase subunits), which are distinct from bacterial systems. While mitochondria in eukaryotes come from a bacterial lineage, the lineage that gave rise to eukaryotes is archaeal in origin, explaining the closer relationship to Archaea. Protista isn’t a separate domain but an informal grouping within Eukarya, so it isn’t the closest domain-level relative.