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Chapter 25.Phylogeny & Systematics

An unexpected family tree. What are theevolutionary relationships among ahuman, a mushroom, and a tulip?Molecular systematics has revealedthat—despite appearances—animals,including humans, and fungi, such asmushrooms, are more closely related toeach other than either are to plants.

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Phylogeny & Systematics Phylogeny

evolutionary history of a species based on common ancestries inferred

from fossil record morphological & biochemical resemblances molecular evidence

Systematics connects classification

system to phylogeny bycategorizing & namingorganisms

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5000 year old ice mummy found on an Alpineridge dividing Austria from Italy at 10,500 feetabove sea level.

Fossil record Sedimentary rock are richest source of

fossils fossil record is a substantial, but

incomplete, chronicle of evolutionaryhistory spotty historical documents of biology

history of life of Earthis punctuated bymass extinctions

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Paleontology Study of fossils

fossils provide the strongestevidence of change

links past & current organismsWoolly mammoth tusks

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Fossils

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Building phylogenies Morphological & molecular homologies

similarities based on shared ancestries bone structure DNA sequences

beware of analogous structures convergent evolution

marsupial mole

placental mole

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Evaluating molecular homologies Aligning DNA

sequences more bases in

common =more closelyrelated

analyzed bysoftware

beware of molecular homologies

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Systematics Connecting

classification tophylogeny hierarchical system Linnaean system binomial system

genus species

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Connectionbetweenclassification& phylogeny

Tracing possible evolutionaryrelationships between someof the taxa of the orderCarnivora, a branch of theclass Mammalia.

Building trees

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Illustrating phylogeny Cladograms

patterns of shared characteristics

Classify organismsaccording to theorder in time atwhich branchesarise along aphylogenetic tree

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Molecular Systematics Hypothesizing phylogenies using molecular

data apply principle of parsimony

simplest explanation fewest evolutionary events

hypothetical birdspecies

3 possiblephylogenies

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Parsimony Choose the “tree” that explains the

data invoking the fewest number ofevolutionary events

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Parsimony & analogy vs. homology

Phylogenetic trees are hypothesesWhich is the most parsimonious tree?

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Modern Systematics Shaking up some trees!

Crocodiles arenow thought tobe closer tobirds thanother reptiles

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Of Mice and Men… Evolving genomes

now that we can compare the entiregenomes 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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Molecular clocksTrace variationsin genomes todate evolutionarychanges

Rate of change iscalculated andthen extrapolateback

What does thisassume?

HIV-1M samples were collected frompatients between early 1980s & late1990s. The gene evolved at a relativelyconstant rate. Concluded that HIV-1Mstrain first infected humans in 1930s.

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Universal Tree of Life 3 Domains

Bacteria Eukarya Archaea