Post on 31-Mar-2015
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Taxonomy & Phylogeny
Classification of Organisms
Classification
• What characters are suitable for classification
• Systematics– Combination of
taxonomy & phylogeny
– Systematic approach to understanding evolutionary relationships among organisms
Hierarchical Classification System
• Taxa– Major groupings or categories– Nested set of increasing inclusiveness
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Cladistic Tree of Life
Wittiker’s 5 Kingdom Classification Scheme
Taxonomic Rules
• Binomial nomeclature– Genus species– Genus name is noun– species name is adjective– Higher taxonomic levels (families, orders, etc..) are
also nouns
Taxonomy Relates to Phylogeny
• Taxonomic characters allow phylogenetic grouping
• Useful taxonomic characters– Morphological – Molecular (biochemical)
• Chromosomal
• Proteins
• DNA
• Homologies– Character similarities attributed to common ancestry
Using Taxonomic Characters to Construct Phylogenies
• Ancestral character state– The form of the trait present in the most recent
common ancestor of the groups being considered
• Derived character state– The variant forms of the trait present in the members
of the groups being considered
• Polarity– Relationship of character trait state to ancestral state
Example of Polarity Determination
• Study group– Amniotes – animals with amniotic membrane around
developing embryo– Birds, Reptiles, Mammals
• Character being studied– Dentition – teeth
• Character states– Present– Absent
• Question: Is dentition a derived or ancestral trait for amniotes?
• Outgroup comparison– Phylogenetically close group, but non-amniote
Example of Polarity Determination
teethteeth
teeth
no teeth
MammalsBirdsReptiles
Amniote
Amphibians&Fish
Non-Amniote
• Outgroup has teeth– therefore teeth are considered ancestral & be presumed to occur in most recent
common ancestor of amniotes and non-amniotes
• Teeth in amniotes is an ancestral character state• Loss of teeth in birds is a derived state
teeth
Common Ancestor
Cladograms
• Clade– Groups of organisms that share derived character
states
• Synapomorphy– Shared, derived character
• Cladogram– Nested, hierarchical assembly and representation of
clades
Phylogenetic Relationships Established by Comparison of Multiple Characters
Cladograms vs Phylogenetic Trees
• Cladogram– Lacks information
• duration of lineages
• Amounts of evolutionary change
• Phylogenetic tree– Establishes extinct vs extant lineages– Indicates evolutionary timescale & degrees of
change• Length of lines or numerical indications
Molecular Phylogeny
Human
• Comparison of cytochrome c mutations
Phylogenetic Groupings
• Monophyletic– All descendents and most recent common ancestor
• Paraphyletic– Leaves out some descendents from a recent common ancestor
• Polyphyletic– Arbitrary groupings which do not include common ancestors
Cladistics & Cladograms vs Traditional Taxonomy
• Cladistics– Taxonomic groupings based solely on establishing
monophyletic relationships– Cladograms establish monophyletic taxonomic levels
• Traditional taxonomy– Common descent – phyletic relationship– Adaptive evolutionary change – ecological zones
Fig. 32.7