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Lecture 09.docx
Lecture_09.docx
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Lecture 09.docx-Lecture 09 Phylogeny Overview o
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Lecture 09.docx-Lecture 09 Phylog...
Lecture_09.docx-Lecture 09 Phylogeny Overview o
Page 1
Lecture 09
Phylogeny Overview
o
Phylogeny
: Evolutionary history of a group of species
Branching diagram
Shows relationships among taxa
Shows patterns of ancestry
Use all possible types of data
o
Phylogenetic trees must be inferred
Reconstructing the path we didn’t see
o
Hierarchal classification is reflected in the branching of phylogenetic trees
o
For the most part, classification represents real history of evolution
o
For the most part, organisms that look more alike are most closely related (but not
always true)
Phylogenetic Tree Terminology
o
Node
(branch point): Represents the common ancestor of lineages
An unresolved node is known as a polytomy
o
Species
or Taxa
: The leaves of the tree (the very ends of the tree)
o
Root
: The beginning of the tree corresponds to the common ancestor for all of the
species in the tree
o
Time
: Y-axis
o
Sister Taxa
: Share an immediate common ancestor and are each other’s closest
relatives
o
Branching Pattern
(Topology
): Informative
Page 2
o
Branch Length
: May or may not be informative
Phylogenetic Trees: More Information
o
Branch tips can be arranged in different ways, but the relationship between nodes
can be the same
o
Monophyletic Group
: Contains common ancestors and ALL descendants
So you should be able to just cut the tree in one place to make the subtree
o
Paraphyletic Group
: Contains common ancestor and some but NOT ALL
descendants
o
Polyphyletic
: Taxa with different relative ancestors
o
Ingroup
: Group of taxa of interest, assumed monophyletic
o
Outgroup
: One or more taxa assumed to be outside the ingroup
How to Build a Phylogenetic Tree
o
Measure as many character traits as possible in the group of organisms
Traits to measure: morphological, behavioral, genetic, etc.
o
When character states all agree, building a tree is easy
Similar Traits
o
Homology
: Similarity due to inheritance of traits from a common ancestor
Ancestral Homology
: Originated in an ancestor of the taxon
Derived Homology
: Evolutionary novelty unique to a clade
Synapomorphy
: Shared derived homology (the characteristic at the
beginning of a branch)
o
Homoplasy
: Similarity that came about separately (not inherited from a common
ancestor)
Page 3
Tree Building Techniques
o
Outgroup Comparisons
Why are Phylogenies Useful/Important?
o
Provide an efficient structure for organizing biodiversity
o
Allow us to develop a conception of the totality of evolutionary history
o
Can help us answer specific questions of how evolutionary changes arose
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