Phylogeny and Systematics

Phylogeny Overview
  • Phylogeny refers to the evolutionary history and relationships among species.
Systematics
  • Definition: The study of classification of organisms and their evolutionary relationships.
    • Taxonomy: Focuses on naming and classifying species.
    • Phylogenetics: Involves forming hypotheses about evolutionary history using phylogenetic trees.
Tools for Determining Evolutionary Relationships
  • Scientists utilize several methods to trace evolutionary relationships:
    • Fossil Records: Preserve evidence of past organisms and their evolutionary changes.
    • DNA Analysis: DNA sequences are compared to determine genetic relationships.
    • Protein Analysis: Similarities and differences in protein structures can indicate evolutionary links.
    • Homologous Structures: Physical features that show common ancestry through their similarities.
Phylogenetic Trees
  • Definition: Diagrams representing the evolutionary history of a group of organisms.
    • Similar to Cladograms, but phylogenetic trees illustrate the amount of evolutionary change over time, often visualized with fossil data.
Cladograms
  • Structure:
    • Each line signifies a lineage.
    • Nodes: Points of branching representing common ancestors.
    • Clades: Group formed by the node and all branches from it, where species share derived characteristics.
    • Root: The original common ancestor of all species represented in the cladogram.
Key Features of Cladograms
  • Sister Taxa: Two clades that arise from the same node.
  • Basal Taxon: A lineage that evolved from the root and has remained unbranched.
  • Synapomorphy: A derived trait shared by members of a clade.
    • Derived Characteristic: A trait that is inherited from the most recent common ancestor of a group.
    • Ancestral Characteristic: A trait that existed before the evolution of the most recent common ancestor.
Outgroup
  • Many cladograms include an outgroup, which is the lineage least closely related to the other organisms in the study.
Group Classifications
  • Monophyletic Group: Contains a common ancestor and all its descendants (considered a clade).
  • Paraphyletic Group: Contains a common ancestor but not all descendants.
  • Polyphyletic Group: Fails to include the most recent common ancestor of its members.
Parsimony Principle
  • When resolving conflicts among evolutionary characters, employ the principle of parsimony:
    • Favor the hypothesis that requires the fewest assumptions regarding DNA changes.
Practice Questions
  1. Identify the common ancestor for butterflies, moths, and flies: Answer: C
  2. Identify the basal taxon: Answer: Beetles
  3. Example of sister taxa: Answer: Butterflies, moths, and flies
  4. Tasks involve examining data tables for trait presence/absence to create cladograms.