Taxonomy and Phylogeny Overview

Taxonomy and Classification of Organisms

• Definition of Taxonomy
  Taxonomy is the science of classifying organisms based on shared characteristics and organizing them in hierarchical categories.

• Historical Method of Classification

  • Initially based on morphological similarity (physical forms and structures).
  • Example: Carolus Linnaeus developed binomial nomenclature (genus and species names).

• Example of Classification

  • Scaly foot organism question: Is it a snake, lizard, or worm?
  • Determines classification based on shared characteristics:
    • Legless lizards vs. snakes:**
    • Characteristics like fused eyelids and a highly mobile jaw indicate it's a lizard.

Levels of Taxonomic Classification

• Hierarchical Structure
  • Domain
  • Most general classification; e.g., all members of the domain Eukarya have eukaryotic cells.
  • Kingdom
  • E.g., Kingdom Animalia, characteristics include heterotrophic metabolism and lack of cell walls.
  • Phylum
  • E.g., Phylum Chordata includes animals with spinal structures.
  • Class
  • E.g., Class Mammalia, characterized by hair and mammary glands.
  • Order
  • E.g., Order Carnivora includes carnivorous mammals, such as felids (cats).
  • Family
  • E.g., Family Felidae includes all cat species.
  • Genus and Species
  • Smallest grouping, e.g., Panthera pardus for leopards.

Modern Taxonomy Principles

• Cladistics

  • Uses shared derived characters to separate organisms into groups based on evolutionary significance.
  • Example distinctions:
  • Mammals based on hair and mammary glands, vs. birds which do not share these traits.

• Phylogenetic Trees and Cladograms

  • Visual representation of evolutionary relationships
  • Show branching of species and shared characteristics:
  • Nodes represent shared derived characteristics.
  • Sister taxa have a common ancestor, but one does not evolve from the other.

Key Concepts in Phylogenetic Analysis

• Out Group

  • Group outside of the study group that helps to root the tree.

• Reading Trees

  • Each branch reflects evolutionary relationships among organisms; older nodes are closer to the root.
  • Polytomy indicates uncertainty in relationships when multiple branches come off a node.

• Molecular Phylogenetics

  • Analyzes genetic data to classify organisms.
  • Looks at genetic similarities and differences to establish evolutionary timelines,
  • Molecular Clock:
  • Predicts divergence times based on genetic changes between species.
  • Example: If two bird species differ at multiple gene loci, this might suggest a divergence 5 million years ago.

Homology vs. Analogy

• Understanding evolutionary relationships requires distinguishing between:
  • Homology: Similar traits due to shared ancestry.
  • Analogy: Similar traits due to convergent evolution (similar adaptations to environmental pressures without common ancestry).