phylogeny and

Taxonomy (Classification of Organisms)

Definition

• Taxonomy: branch of biology that classifies organisms based on shared characteristics.

• Uses hierarchical groups called taxa (singular: taxon).

Taxonomic Hierarchy (Broad → Specific)

1. Kingdom

2. Phylum

3. Class

4. Order

5. Family

6. Genus

7. Species

• As you move down → fewer organisms, more specific traits.

Carolus Linnaeus (1700s)

• Father of taxonomy.

• Originally classified organisms into:

  • Plants

  • Animals

• Created binomial nomenclature.

Binomial Nomenclature (Scientific Naming)

Rules

• Two-part scientific name:

  • Genus (capitalized)

  • species (lowercase)

• Written in italics (or underlined if handwritten).

Example: Humans

• Kingdom: Animalia

• Phylum: Chordata

• Class: Mammalia

• Order: Primates

• Family: Hominidae

• Genus: Homo

• Species: sapiens

• Scientific name: Homo sapiens

Limitations of Linnaean System

• Based mainly on physical traits.

• Does not show evolutionary relationships.

• Artificial ranking can suggest false relatedness.

Whittaker’s Five-Kingdom System

Improved Classification

Recognized cell type and organization.

Five Kingdoms

• Monera → prokaryotes (bacteria)

• Protista → simple eukaryotes

• Fungi

• Plantae

• Animalia

Key Contribution

• Distinguished:

  • Prokaryotic cells

  • Eukaryotic cells

Phylogeny (Evolutionary Relationships)

Definition

• Study of evolutionary history and relationships among organisms.

• Groups organisms based on common ancestry.

Key Concept

• Organisms grouped into clades based on shared derived traits.

Advantages Over Linnaean System

• Shows evolutionary history.

• Does not rank organisms artificially.

• Reveals true relationships.

Examples

• Crocodiles and birds closely related.

• Fungi more related to animals than plants.

Phylogenetic Tree (Tree of Life)

Definition

• Diagram showing evolutionary relationships of organisms.

• Covers ~3.5 billion years of evolution.

What It Shows

• Speciation events.

• Common ancestors.

• Lineage changes over time.

Scientific Uses

• Understand evolution.

• Improve agriculture.

• Develop medical treatments.

• Study invasive species.

Important Idea

• Phylogenetic relationships = time since common ancestor (not just similarity).

Cladistics

Definition

• Method of classifying organisms based on shared inherited traits.

• Determines evolutionary relationships.

Characters Used

• Physical traits

• Behavioral traits

• Physiological traits

• Molecular traits (DNA)

Shared Derived Characters

• Traits that evolved in recent ancestors.

• Used to group organisms.

Clade

• Group consisting of:

  • Common ancestor

  • All descendants.

• Example: reptiles + birds form a clade.

Cladistic Analysis

• Compares organisms’ traits.

• Identifies evolutionary branching.

• Determines sequence of trait evolution.

Speciation

• Occurs when populations develop new distinguishing traits.

• Leads to new species.

Cladogram

Definition

• Branching diagram showing evolutionary relationships.

Key Parts

• Node → common ancestor; speciation event.

• Branches → evolutionary lineages.

• Tips → descendant species/groups.

• Sister groups → share most recent common ancestor.

Purpose

• Shows order of evolutionary events.

• Shows relatedness, not exact time.

Cladogram vs Phylogenetic Tree

• Cladogram → shows relationships only.

• Phylogenetic tree → shows relationships + evolutionary time.

Creating a Cladogram

Steps

1. Identify organisms.

2. List shared and unique traits.

3. Determine which traits evolved first.

4. Construct branching diagram.

Important Principle

• Traits evolve due to environmental pressures.

• Leads to adaptation and speciation.

Example

• Darwin’s finches → beak changes from food sources.

Core AP Bio Terms to Memorize

• Taxonomy

• Taxon

• Binomial nomenclature

• Phylogeny

• Clade

• Shared derived character

• Cladistics

• Cladogram

• Node

• Sister groups

• Speciation

• Common ancestor