Phylogeny
description
Transcript of Phylogeny
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
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
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
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
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
ParsimonyThe simplest explanation consistent with the data.The smallest number of evolutionary changes needed to explain a phylogenetic tree (cladogram).
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Phylogenetic trees are hypothesis .
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.
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…!!
OUTGROUP
Examples
OUTGROUP