Systematics, Taxonomy and Cladistics

Introduction to Systematics

• Systematics classifies organisms based on shared characteristics and evolutionary relationships.
• All organisms share common traits such as cellular composition, ATP energy transfer, and DNA hereditary information encoding.

Phylogeny and Evolutionary Relationships

• Phylogeny represents a hypothesis about the relationship patterns among species.
• Charles Darwin proposed "Descent with Modification", explaining species change over generations

Cladistics and Cladograms

• A Cladogram is a diagram illustrating evolutionary relationships among organisms.
• Branch points (nodes) in a Cladogram signify common ancestors, showing divergence points in evolutionary history.

Taxonomy and Classification

• Taxonomy is the science of classifying organisms using a hierarchical system of Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.
• Carl Linnaeus is considered the father of modern taxonomy because of his development of the binomial nomenclature system.
• Binomial Nomenclature is a two-part scientific naming system, like Homo sapiens.

Domains and Kingdoms

• The three Domains of Life are:
  • Bacteria: Prokaryotic, unicellular organisms containing peptidoglycan cell walls.
  • Archea: Prokaryotic, unicellular organisms, found in extreme environments, possessing unique cell membranes.
  • Eukarya: Eukaryotic organisms including protists, fungi, plants, and animals
• Kingdoms within Eukarya:
  • Protista: Diverse group of mostly unicellular organisms.
  • Fungi: Multicellular (except yeasts), decomposers.
  • Plantae: Multicellular, photosynthetic organisms.
  • Animalia: Multicellular, heterotrophic organisms.

Homology vs. Analogy

• Homologous Structures are similar structures due to shared ancestry, evident in vertebrate forelimbs of humans and bats.
• Analogous Structures serve similar functions but have different evolutionary origins, exemplified by wings in birds and insects.

Molecular Systematics

• Molecular Systematics uses DNA, RNA, and protein sequences to ascertain evolutionary relationships.
• Ribosomal RNA (rRNA) is vital in molecular phylogenetics because its sequences change slowly, useful for studying long-term evolutionary relationships.

Evolutionary Concepts in Systematics

• A Monophyletic Group (Clade) includes a common ancestor and all its descendants.
• A Paraphyletic Group includes a common ancestor but not all descendants.
• A Polyphyletic Group includes species with different ancestors.
• The Principle of Parsimony dictates that the simplest explanation should be preferred in phylogenetic analysis.

Horizontal Gene Transfer (HGT)

• Horizontal Gene Transfer is the movement of genes between different species.
• HGT is common in prokaryotes and can complicate phylogenetic trees.

Evolutionary Trees and Time Estimation

• Molecular Clocks estimate evolutionary divergence times based on mutation rates.
• Fossils provide historical records that validate phylogenetic hypotheses.

Comparison of Archea, Bacteria and Eukarya

• Amino acid that initiates protein synthesis:
  • Archaea uses Methionine.
  • Bacteria uses Formylmethionine.
  • Eukarya uses Methionine.
• Introns:
  • Archaea have introns present in some genes.
  • Bacteria have introns that are absent.
  • Eukarya have introns that are present.
• Membrane-bounded organelles:
  • Archaea have few.
  • Bacteria have few.
  • Eukarya have present.
• Membrane lipid structure:
  • Archaea has a branched structure.
  • Bacteria has an unbranched structure.
  • Eukarya has an unbranched structure.
• Nuclear envelope:
  • Archaea has an absent nuclear envelope.
  • Bacteria has an absent nuclear envelope.
  • Eukarya has a present nuclear envelope.
• Number of different RNA polymerases:
  • Archaea has several.
  • Bacteria has one.
  • Eukarya has several.
• Peptidoglycan in cell wall:
  • Archaea has an absent peptidoglycan in cell well.
  • Bacteria has a present peptidoglycan in cell wall.
  • Eukarya has an absent peptidoglycan in cell wall.
• Response to antibiotics:
  • Archaea's growth is not inhibited.
  • Bacteria's growth is inhibited.
  • Eukarya's growth is not inhibited.

Explore systematics, taxonomy, and cladistics for classifying organisms based on shared traits and evolutionary relationships. Learn about phylogeny, cladograms, and the taxonomic hierarchy from Domain to Species. Understand how these tools represent species divergence and common ancestry.