Practice question

Carl Woese established revolutionary three-domain classification based on comparative analysis of small subunit ribosomal RNA 16S and 18S sequences supplemented by ribosomal proteins, RNA polymerase subunits, and elongation factors considered refractory to horizontal transfer. By oligonucleotide catalog comparisons he demonstrated deep divergence between bacteria and archaebacteria later renamed Archaea, distinct from eukaryotic 18S rRNA. Phylogenetic trees constructed using slowly evolving positions revealed three primary aboriginal lines. Molecular chronometer approach superseded morphological five kingdom system, emphasizing genetic relatedness, conserved signature sequences, and informational gene phylogeny for domain definition.