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Phylogeny and the Tree of Life

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Phylogeny and the Tree of Life Chapter 26 Phylogeny What is phylogeny? The evolutionary history of a group Systematics attempts to reconstruct phylogeny, by analyzing ... – PowerPoint PPT presentation

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Title: Phylogeny and the Tree of Life


1
Phylogeny and the Tree of Life
  • Chapter 26

2
Phylogeny
  • What is phylogeny?
  • The evolutionary history of a group
  • Systematics attempts to reconstruct phylogeny, by
    analyzing evolutionary relatedness
  • Use morphological and biochemical similarities
  • Molecular systematics uses DNA RNA and proteins
    to infer evolutionary relatedness
  • Different tools are used to reconstruct
    phylogenies

3
Systematics
  • Uses evidence from fossil record and existing
    organisms to reconstruct phylogeny
  • Use branching taxonomic categories such that they
    reflect phylogeny
  • Binomial nomenclature Genus species keeps
    identity of organism universal
  • Other taxa Domain, Kingdom, Phylum, Class,
    Order, Family Genus, species

4
Taxonomy
5
Cladistics
  • Cladogram is a tree with two way branch points
  • Each branch point represents divergence from
    common ancestor
  • Each branch is called a clade
  • Clades are monophyletic

6
Phenetics
  • Phenetics
  • compares many anatomical characteristics to
    (overall phenotype) to construct phylogeny
  • Does not sort homologous from analogous
    structures.
  • phylogenetic trees

7
Monophyletic vs. Polyphyletic Taxa
  • Monophyletic single ancestor gave rise to all
    species in the taxon
  • Polyphyletic taxon whose members derive from 2
    or more different ancestors
  • Paraphyletic excludes species that share the
    common ancestor
  • Creating the ideal monophyletic taxa is not
    always easy

8
Not all Similarities Represent Common Ancestry
  • Homologous structures indicate shared common
    ancestry
  • Homologous structures are therefore evidence of
    divergent evolution
  • Analogous structures are similar in function but
    not in evolutionary history
  • Analogous structures are evidence of convergent
    evolution
  • It is not always easy to sort homologous from
    analogous structures

9
  • How do we differentiate between homologous and
    analogous structures?
  • Compare embryonic development of the structures
    in question
  • Look for structures that are complex
  • The more complex the structures are the more
    likely that they are homologous
  • Compare macromolecules along with anatomical
    features

10
How would you compare the fins in these 2
organisms?
11
In what way are these organisms displaying
examples of convergent evolution?
12
Cladistics
  • Cladistics
  • sorts homologous from analogous structures
  • sorts primitive and shared derived
    characteristics

13
Shared Derives Characteristics
  • Need to differentiate between shared primitive
    characters and shared derived characters

Analogies
All similar characters
Primitive (ancestral)
Homologies
Derived (unique to a clade)
14
Outgroups
  • Distinguishes between shared primitive and shared
    derived characteristics
  • Closely related to ingroup

15
Performing Outgroup Comparison
What is the shared ancestral characteristic?
Notochord
Does not mean that turtles evolved more recently
than salamander
16
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17
Maximum Parsimony and Maximum Likelihood
  • Maximum parsimony
  • Simplest explanation consistent with facts
  • Maximum likelihood
  • Use most likely sequence of events to explain
    evolutionary changes
  • If we assume DNA changes occur at equal rates
    among all organisms then.

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19
Four Species Problem
20
After analyzing DNA sequences and mutations, this
tree is the simplest explanation of the changes
21
  • And sometimes the simplest explanation is not the
    best

22
Which is more correct?
Parsimony does not always work, nature does not
always take the simplest course
23
Modern Systematics
24
Hominidae
Pongidae
Classical Taxonomy
Hominidae
Pongidae
Cladistic Taxonomy
25
Molecular Clocks
  • Proteins and mitochondrial genomes have constant
    rate of change over time
  • Use these rates to determine relative
    evolutionary relatedness.
  • Accuracy of these clocks is still debated
  • Recently used to date origin of HIV

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The End!
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