BIOL1020 - Lecture 14 - Phylogeny and Phylogenetic Trees

Phylogeny Overview

  • Definition: Study of the evolutionary history and relationships between organisms.
  • Key Concepts:
    • Phylogenetic relationships help understand which organisms evolved from others and their shared ancestry.
    • These relationships do not necessarily indicate how organisms are similar or different.

Phylogenetic Tree

  • Diagram: Summarizes the evolution of various living organisms on Earth.
  • Purpose: Illustrates evolutionary pathways and relationships based on genetic or physical traits.

Structure of a Phylogenetic Tree

  • Components:
    • Nodes: Represent ancestors and points of divergence in evolution.
    • Branches: Indicate evolutionary order but not elapsed time between divergences.

Construction of Phylogenetic Trees

  • Types of Trees:
    • Rooted Phylogenetic Tree: Shows a common ancestor at the base with branches diverging from a single point.
    • Unrooted Phylogenetic Tree: Displays relationships among species without showing a common ancestor.
  • Common Features:
    • Branch points indicate where lineages diverged.
    • Sister taxa: Two lineages stemming from the same branch point.
    • Basal taxon: A lineage that remains unbranched and diverged early from the root.
    • Polytomy: A branch with more than two lineages, indicating unresolved relationships.

Evolutionary Pathways

  • The tree aids in tracing the pathway from the base to any individual species.
  • Understanding common ancestry helps identify lineages.

Importance of Phylogeny

  • Contributes to biological sciences like systematics, taxonomy, paleontology, and genetics.
  • Helps in the discovery of medicinal plants and understanding evolutionary relationships.

Data Sources for Phylogeny

  • Fossils, structural data, molecular evidence, and DNA analysis contribute to constructing phylogenetic trees.
  • Trees are dynamic; they evolve as new information emerges.

Practical Applications

  • Example: Dalbergia sissoo shares a DNA marker with species in the Fabaceae family and has identified antifungal properties.
  • Phylogeny guides the discovery of compounds for medicinal applications.

Character Traits in Phylogeny

  • Shared Ancestral Character: Present in the ancestors of a group, e.g., the vertebrate in the clade Vertebrata.
  • Shared Derived Character: Evolved in a group and not found in all ancestors, e.g., amniotic eggs in Amniota.

Clade Construction

  • Clades are groups of organisms descended from a common ancestor, arising from a specific branch point.
  • Importance of clades: They help to categorize the varying sizes of groups and their evolutionary relationships.

Challenges in Phylogeny Construction

  • Difficulty in establishing connections among organisms, especially with homologous and analogous structures.
  • The need for maximum parsimony: Finding the simplest, most obvious evolutionary pathway minimizes complexity.

Evolutionary Relationships and Technology

  • Modern DNA sequence analysis and computer algorithms enhance phylogenetic tree construction.
  • Alternative representations of evolutionary relationships include the web of life and ring of life diagrams.

Key Takeaway

  • Phylogenetic trees are crucial in understanding evolutionary relationships and biology as a whole, helping scientists trace lineages and relationships among diverse organisms over time.