1. Phylogeny & Systematics
Chapter 25.
Phylogeny & Systematics
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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2. “Homoplasies” Building phylogenies
Morphological & molecular homologies
similarities based on shared ancestries
bone structure
DNA sequences
beware of analogous structures
convergent evolution
“Homoplasies”
marsupial mole
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placental mole

3. Evaluating molecular homologies
Aligning DNA sequences
more bases in common = more closely related
analyzed by software
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beware of molecular homologies

4. Orthologous genes
Common genes: differences due to speciation; diverged after a speciation event
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5. Paralogous Genes Common genes; differences due to a duplication event
Examples: next page
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6. Ortho/Para Genes example:
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7. Building trees Connection between classification & phylogeny
Tracing possible evolutionary relationships between some of the taxa of the order Carnivora, a branch of the class Mammalia.
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8. 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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9. Illustrating phylogeny
Cladograms
patterns of shared characteristics
Shared Primitive Character
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10. Illustrating phylogeny
Cladograms
patterns of shared characteristics
Shared Derived Character
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11. Parsimony & analogy vs. homology
Phylogenetic trees are hypotheses
Which is the most parsimonious tree?
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12. Parsimony & analogy vs. homology
Maximum Parsimony
Maximum
Liklihood
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13. Modern Systematics Shaking up some trees!
Crocodiles are now thought to be closer to birds than other reptiles
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14. Of Mice and Men… Evolving genomes
now that we can compare the entire genomes of different organisms, we find…
humans & mice have 99% of their genes in common
50% of human genes have a close match with those of yeast!
the simplest eukaryote
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15. Molecular clocks
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.
Trace variations in genomes to date evolutionary changes
Rate of change is calculated and then extrapolate back
What does this assume?
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16. Trees: Phylogram (Primates)
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17. Tree: Phylogram (Giraffe species)
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18. Tree: Ultrametric
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19. Universal Tree of Life
3 Domains
Bacteria
Eukarya
Archaea
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