Domains
The Eubacteria of Kingdom Monera, commonly called bacteria:
1. Prokaryotic organisms without a nuclear membrane
2. Eubacterial rRNA and no introns in genome
3. Membrane lipids are primarily diacyl glycerol ethers
4. Cell walls contain thick (gram+) or thin layers of peptidoglycan (gram-)
The Archaea, or Archaeobacteria
1. Prokaryotic organisms without a nuclear membrane
2. Archaeobacterial rRNA – introns in genome
3. Membrane lipids are unusual – primarily isoprenoid glycerol diether or diglycerol tetraether derivatives
4. The cell wall does not contain peptidoglycan (gram-)
There are three groups of Archaea, which also called extremophiles: Methanogens are poisoned by O2, Thermophiles live in extreme temperatures, and Halophiles live in highly saline environments
1. Nuclear membrane
2. Membrane bound chloroplasts (plants) and/or mitochondria (animals)
Modern eukaryotic cells appear to have arisen from a prokaryotic cell about 1.4 billion years ago. The serial endosymbiosis theory, first proposed by Lynn Margulis, is widely accepted as explanation for the resemblance between prokaryotes and eukaryotic organelles.
1 Glossary:
Taxonomies aim to group organisms according to shared characteristics against the background of biological diversity.
Phenetic system: groupings of organisms based on mutual similarity of phenotypic (physical and chemical) characteristics. Phenetic groupings may or may not correlate with evolutionary relationships.
Numerical Taxonomy: a common approach to phenetic taxonomy, which employs a number of phenotypic characteristics to generate similarity coefficients that may be mapped in dendrograms. Groupings based on numerical taxonomy may or may not correlate with evolutionary relationships.
Phylogenetic system: groups organisms based on shared evolutionary heritage. DNA and RNA sequencing techniques are considered to give the most meaningful phylogenies.
Monophyletic taxon or clade: an accurate grouping of only (opp. polyphyletic) and all (opp. paraphyletic) descendents of a shared common ancestor. A monopyletic group is genetically homogeneous and reflects evolutionary relationships.
Paraphyletic taxon or clade: a monophyletic group that excludes one or more discrete groups descended from the most recent common ancestral species of the entire group. Other descendent species of the most recent common ancestor have been excluded from the paraphyletic taxon, usually because of morphologic distinctiveness.
Polyphyletic taxon: opposite to monophyletic taxon: A polyphyletic group is mistakenly or improperly erected on the basis of homoplasy.—characteristics that have arisen despite not sharing a common ancestor. Homoplasy arises because of convergent evolution, parallelism, evolutionary reversals, horizontal gene transfer, or gene duplications. Polyphyletic taxa are genetically heterogeneous because members do not share a common ancestor.
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