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Phylogeny

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

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Phylogeny

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  1. 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 • not necessarily an evolutionary implication www.diogenesii.files.wordpress.com/.../image016.jpg

  2. ancient modern • Systematics = scientific study of biological diversity in an evolutionary context • includes: morphological, molecular genetic, biochemical, physiological, ecological traits • 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 Graham et al. 2009

  3. Monophyletic group is a taxon (group of organisms) which forms a clade, meaning that it consists of an ancestor and all its descendants. Monophyletic group

  4. Derived Characters • primitive and derived are relative and 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

  5. 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 Analogous All similar characters Ancestral Homologous 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

  6. 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

  7. Parsimony The 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 .

  8. 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.

  9. 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…!!

  10. OUTGROUP

  11. Examples OUTGROUP

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