Download Chapter 25.

Chapter 25.
Phylogeny & Systematics
AP Biology
An unexpected family tree. What are the
evolutionary relationships among a
human, a mushroom, and a tulip?
Molecular systematics has revealed that—
despite appearances—animals, including
humans, and fungi, such as mushrooms,
are more closely related to each other
than either are to plants.
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Building phylogenies
 Morphological & molecular homologies

similarities based on shared ancestries
 bone structure
 DNA sequences

beware of analogous structures
 convergent evolution
“Homoplasies”
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marsupial mole
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placental mole
Evaluating molecular homologies
 Aligning DNA
sequences
more bases in
common =
more closely
related
 analyzed by
software

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beware of molecular homologies
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Orthologous genes
Common
genes:
differences
due to
speciation;
diverged after
a speciation
event
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Paralogous Genes
 Common genes; differences due to a
duplication event
Examples: next page
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Ortho/Para Genes example:
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Building trees
 Connection
between
classification
& phylogeny
Tracing possible evolutionary
relationships between some
of the taxa of the order
Carnivora, a branch of the
AP
Biology
class
Mammalia.
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Illustrating phylogeny
 Cladograms

patterns of shared characteristics
Classify organisms
according to the
order in time at which
branches arise along
a phylogenetic tree
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Illustrating phylogeny
 Cladograms

patterns of shared characteristics
Shared Primitive
Character
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Illustrating phylogeny
 Cladograms

patterns of shared characteristics
Shared Derived
Character
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Parsimony & analogy vs. homology
Phylogenetic trees are hypotheses
Which is the most parsimonious tree?
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Parsimony & analogy vs. homology
Maximum
Parsimony
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Maximum
Liklihood
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Modern Systematics
 Shaking up some trees!
Crocodiles are
now thought to
be closer to
birds than other
reptiles
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Molecular clocks
Trace variations in
genomes to date
evolutionary
changes
HIV-1M samples were collected from
patients between early 1980s & late
1990s. The gene evolved at a relatively
constant rate. Concluded that HIV-1M
strain first infected humans in 1930s.
Rate of change is
calculated and
then extrapolate
back
What does this
assume?
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Trees: Phylogram (Primates)
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Tree: Phylogram (Giraffe species)
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Tree: Ultrametric
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Universal Tree of Life
 3 Domains
Bacteria
 Eukarya
 Archaea

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