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SYSTEMATICS
• The study of biological diversity in an
evolutionary context
• encompasses both taxonomy and phylogeny
Taxonomy
• Two main objectives:
– to sort out organisms into species
– to classify species into higher taxonomic levels
• Species that appear to be closely related are grouped
into the same genus.
• the leopard, Panthera pardus, belongs to a genus
that includes the African lion (Panthera leo) and the
tiger (Panthera tigris).
• Taxon = a named taxonomic unit at any
level; (taxa = plural)
– ex: Mammalia is a taxon at the Class level
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TAXONOMY
• taxonomic system developed by Linnaeus in
the 18th century
– binomial = Genus species
– classification system
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Domain
Kingdom
Phylum
Class
Order
Family
Genus
species
Eukarya
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
sapiens
Limitations of the Linnean System
Many hierarchies are being re-examined based on
the results of molecular analysis
-Linnaean taxonomy does not take into account
evolutionary relationships
-The phylogenetic and systematic revolution is
underway
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PHYLOGENY
• Hypothesis of the evolutionary history of a
group
• represented by pictures: phylogenetic trees
– time goes from the bottom up
– read from bottom up, NOT LEFT TO RIGHT
– branch “length” = the number of changes
Phylogenies depict evolutionary relationships
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• Phylogenetic trees reflect the hierarchical classification
of taxonomic groups nested within more inclusive
groups.
Fig. 25.8
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Approaches to Constructing
Phylogenies
• Cladistics
– uses shared derived characteristics
(synapomorphies) to classify organisms
– Not shared ancestral characteristics, not overall
similarity
• Because evolution is not steady paced, not
unidirectional, may be convergent
Cladistics
Examples of ancestral versus derived characters
• Presence of hair is a shared derived feature of
mammals
• Presence of lungs in mammals is an ancestral
feature; also present in amphibians and reptiles
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Cladistics
A Cladogram; DNA
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Cladistics
A Cladogram: DNA
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Approaches to Constructing
Phylogenies
• Traditional approaches
– Used overall similarities
– Characters are weighted by the taxonomist
PHYLOGENY
• systematists prefer monophyletic taxa
– a single ancestor gave rise to all species in that
taxon and to no species in any other taxa
Systematics and Classification
Monophyletic Group
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Systematics and Classification
Paraphyletic Group
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Systematics and Classification
Polyphyletic Group
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Systematics and Classification
Old plant classification system
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Systematics and Classification
New plant classification system
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Evidence used to reconstruct
phylogenies
• Comparative anatomy, morphology,
embryology, etc.
– problems of homology vs homoplasy (analogy)
• homology = likeness due to common ancestry
• homoplasy or analogy = likeness due to convergent
evolution
Comparative Biology
Distribution of saber-toothed mammals
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Can Have
Homoplastic Molecular Data
A Cladogram: DNA
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Evidence used to reconstruct
phylogenies
• Protein comparisons
• DNA comparisons
– DNA-DNA hybridization, restriction mapping,
DNA sequencing
Character Mapping
• Once you have a phylogeny you can trace
the evolution of characters or traits in that
group
• use the rules of parsimony
– the simplest is the best
Parsimony and Homoplasy
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Phylogenetic Trees are Hypotheses
Grouping Organisms
Carl Woese proposed a six-kingdom system
Prokaryotes
Eukaryotes
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KINGDOMS
• Monera = Archaebacteria & Eubacteria
– prokaryotic
• Protista
– eukaryotic
• Plantae
– eukaryotic, multicellular, autotrophic, cell walls
• Fungi
– eukaryotic, multicellular, heterotrophic, cell walls
• Animalia
– eukaryotic, multicellular, heterotrophic, no cell walls
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