(3) Unit 7 Topic 9 Packet

Unit 7: Topic 9 - Phylogeny

Introduction to Phylogeny

• Systematics: Classification of organisms and their evolutionary relationships.

• Taxonomy: The naming and classification of species.

• Phylogenetics: Hypothesis of evolutionary history; uses phylogenetic trees to illustrate evolution.

  • Example: Charles Darwin’s early phylogenetic trees.

Types of Information for Determining Relationships

• Sources Used:

  • Fossil records

  • DNA

  • Proteins

  • Homologous structures

• Trustworthiness: DNA and proteins provide the most reliable insight into evolutionary history compared to fossil records and homologous structures.

Phylogenetic Trees vs. Cladograms

• Phylogenetic Trees:

  • Complex diagrams representing the evolutionary history of organisms.

  • Show the amount of evolutionary change over time, often measured by fossils.

• Cladograms:

  • Simplified representations focusing on branching patterns without measuring change over time.

  • Each line represents a lineage.

  • Nodes represent common ancestors for groups of species (clades).

Basic Vocabulary in Cladograms

• Lineages: Each branch in a cladogram.

• Nodes: Points where branches split, representing common ancestors.

• Clades: Groups of species that include their common ancestor and all descendants.

  • Example: A clade can include tigers, snow leopards, leopards, lions, and jaguars all sharing a common ancestor.

• Root: The base of the tree representing the common ancestor of all species in the cladogram.

Advanced Vocabulary in Cladograms

• Sister Taxa: Two clades that emerge from the same node.

• Basal Taxon: A lineage that evolved from the root and remains unbranched.

• Derived Characters: Traits shared by members of a clade, denoting evolutionary changes:

  • Synapomorphies: Derived traits shared among clade members.

  • Ancestral Characteristics: Traits that existed before the common ancestor of the group.

• Outgroup: A lineage least closely related to the other organisms; serves as a point of comparison in cladistics.

Types of Groups in Cladograms

1. Monophyletic Group: Includes the most recent common ancestor and all descendants.

2. Paraphyletic Group: Includes the most recent common ancestor but not all descendants.

3. Polyphyletic Group: Does not include the most recent common ancestor of all members.

Principle of Parsimony

• Definition: When constructing cladograms, choose the hypothesis that necessitates the fewest assumptions. Aims to minimize the number of changes needed to explain the evolutionary relationships among species.

Constructing Cladograms: Practical Examples

• Step-By-Step Process:

  • Identify the outgroup (least related lineage).

  • Determine which traits are present or absent in species.

  • Assign traits to branches, representing their evolutionary appearance (derived traits).

  • Label clades and nodes accurately.

Practice Problems

• Exercises Include: Constructing and identifying examples on cladograms using data tables about species and traits.

• Key Strategies: Understand how to identify sister taxa, basal taxa, and outgroups while constructing or interpreting cladograms.