Cladistics and Classification

State why classification of organisms is needed

• Organizes global biodiversity
• Helps identify new species
• Supports evolution, medicine, and conservation

Explain why classification helps conservation

• Knowing a species exists is needed to protect it
• Misclassification can hide endangered species

Explain the problems with using morphology for classification

• Similar traits don’t always mean related
• Example

List the main taxonomic ranks in order

• Domain
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Recall a mnemonic to remember taxonomic ranks

• Dear King Phillip Came Over For Great Soup

State one limitation of traditional taxonomy

• Doesn't always match evolutionary patterns

Explain what a clade is

• Group with a common ancestor
• All descendants included

Distinguish between a clade and a taxon

• Clade = evolutionary group
• Taxon = named group (may not be a clade)

Explain how DNA sequencing helps classification

• More accurate than appearance
• Shows real genetic relationships

State why classification is sometimes changed

• New DNA evidence reveals errors
• Some groups were based only on appearance

Explain how cladistics changed taxonomy

• Uses clades instead of ranked taxa
• Based on shared DNA or amino acids

Define a monophyletic group

• Includes all descendants of a common ancestor

Describe evidence used to form clades

• DNA base sequences
• Amino acid sequences
• Morphology (less reliable)

State why morphology can mislead cladistics

• Convergent evolution causes similar traits in unrelated species

Define primitive trait

• Trait all members of a clade share
• Evolved early (e.g. spinal cords in vertebrates)

Define derived trait

• Trait found in some clade members
• Evolved later (e.g. feathers in birds)

Explain what a molecular clock is

• DNA mutations happen at steady rate
• More differences = longer time since split

State what affects mutation rate

• Generation time
• Population size
• Natural selection pressure

Define DNA hybridization

• DNA from two species combined
• Fewer mismatches = more closely related

State what a node on a cladogram shows

• A shared common ancestor

Define root, node, and terminal branch in cladograms

• Root

Explain how sequence data builds cladograms

• DNA and amino acids compared
• Similar = closely related
• Used to find order and time of divergence

Define the principle of parsimony

• Simplest tree is most likely
• Fewest evolutionary changes

Explain why cladograms are hypotheses

• Based on current evidence
• May change with new data

Describe what numbers on cladogram branches mean

• Show mutation count
• Used to estimate time (molecular clock)

Explain why cladograms may change over time

• New DNA data = better evidence
• Old traits might have misled earlier models

Describe what happened with figwort family reclassification

• DNA showed it wasn’t a true clade
• Group was split, merged, and reorganized

State why reclassification is an example of falsification

• Old idea based on traits was replaced by DNA evidence

Define convergent evolution

• Different species evolve similar traits
• Not from shared ancestry

State the three domains of life

• Archaea
• Eubacteria
• Eukaryotes

Compare Archaea and Bacteria

• Both are prokaryotes
• Archaea have different cell wall, membrane, and genes

State why Archaea are closer to Eukaryotes than Bacteria

• Similar ribosomes
• Share some genes and lip