phylogeny
DESCRIPTION
Phylogeny. Phylogeny (Greek: phylon (tribe) and genesis (birth)) = classification of organisms using “trees” to order ancestors → descendants Taxonomy = practice of identifying & categorizing organisms classification scheme historically based on morphological features - PowerPoint PPT PresentationTRANSCRIPT
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Phylogeny Phylogeny (Greek: phylon (tribe) and genesis (birth)) =
classification of organisms using “trees” to order ancestors → descendants
Taxonomy = practice of identifying
& categorizing organisms o classification schemeo historically based on
morphological featureso not necessarily an
evolutionary implication
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Systematics = scientific study of biological diversity in an evolutionary contexto includes: morphological, molecular genetic, biochemical, physiological,
ecological traitso CLADISTICS is a form of biological systematics that classifies
organisms into hierarchical monophyletic groups. For statistical hypothesis testing → SIMPLEST TREE- size of clades will vary- more characters will “strengthen” the tree
ancient modern
Graham et al. 2009
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Monophyletic group is a taxon (group of organismsorganisms) which forms a clade, meaning that it consists of an ancestor and all its descendants.
Monophyletic group is a taxon (group of organismsorganisms) which forms a clade, meaning that it consists of an ancestor and all its descendants.
Monophyletic groupMonophyletic group
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Derived Characters
primitive and derived are relativeand only have meaning when placed in context shared, derived characters = synapomorphies a derived character in one group might be primitive in another e.g., fur among tetrapods (4-footed vertebrates) = derived, but…
fur among mammals = primitive
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Shared derived characters
Character: any feature exhibited by a taxon Homologous characters are used to construct cladorgrams
Shared primitive character: homology common to a more inclusive taxon Shared derived character: a unique evolutionary novelty in a clade
All similar characters
Analogous
HomologousAncestral
Derived
Example: backbone vs hair• not all animals posses hair, but all mammals –who have hair as a unique character also have a backbone, a trait shared with all other vertebrates
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Constructing a Phylogeny
Select a focal group
Identify characters to be used in the analysis- ancient vs. derived
Determine the outgroup (i.e., the group that most closely resembles the ancient condition)
Construct a phylogenetic tree
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ParsimonyThe simplest explanation consistent with the data.The smallest number of evolutionary changes needed to explain a phylogenetic tree (cladogram).
Sites 2-4
Sites 5-6
Site 7
Phylogenetic trees are hypothesis .
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Phylogenetic trees are hypotheses
Sometimes most parsimonious tree does not reflect a true phylogeny.
There are more shared primitive characters between lizards and birds, than birds with mammals.
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Remember… Ancient/primitive SIMPLE!!
A character can NOT be gained → lost → gained…
Focus on conserved cf. plastic character traits - flower color is plastic: mutates → changes readily from one
generation to the next
THINK OUTSIDE THE BOX…!!
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OUTGROUP
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Examples
OUTGROUP