Transcript Ch268thed

Phylogeny and the Tree of Life
Chapter 26
Phylogeny
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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
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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
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Taxonomy
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
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Phenetics
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Phenetics =
◦ compares many anatomical characteristics to
(overall phenotype) to construct phylogeny
◦ Does not sort homologous from analogous
structures.
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phylogenetic trees
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
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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
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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
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How would you compare the fins in
these 2 organisms?
In what way are these organisms displaying
examples of convergent evolution?
Cladistics
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Cladistics
◦ sorts homologous from analogous structures
◦ sorts primitive and shared derived
characteristics
Shared Derives Characteristics
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Need to differentiate between shared
primitive characters and shared derived
characters
All similar
characters
Analogies
Primitive
(ancestral)
Homologies
Derived
(unique to
a clade)
Outgroups
Distinguishes between shared primitive
and shared derived characteristics
 Closely related to ingroup
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Performing Outgroup Comparison
What is the shared ancestral characteristic?
Notochord
Does not mean that turtles evolved more recently than salamander
Maximum Parsimony and Maximum
Likelihood
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Maximum parsimony
◦ Simplest explanation consistent with facts
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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….
Four Species Problem
After analyzing
DNA sequences
and mutations, this
tree is the simplest
explanation of the
changes
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And sometimes the simplest explanation
is not the best…
Which is more correct?
Parsimony does not always work, nature does
not always take the simplest course
Modern Systematics
Hominidae
Pongidae
Classical
Taxonomy
Hominidae
Cladistic
Taxonomy
Pongidae
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!