Chapter 25: Phylogeny and Systematics

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Chapter 25Phylogeny andSystematics
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Taxonomy is the division of organisms into
categories based on similarities and
differences. p. 495, Campbell Reece (2005)
Shown is a phylogenetic tree
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Fossil Record

• Fossils are preserved remnants of organisms that
  lived in the past
• Fossils form in sedimentary rock, the oldest
  fossils in the lower strata and younger on the
  upper strata
• Fossil record is incomplete and favors larger
  organisms, those with hard bodies or parts, those
  that were abundant and widespread.

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Fossils
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Morphological Evidence

• Homology- similarity due to common ancestry (same
  structure different function) wing of bat, arm
  of human, flipper of whale
• Analogy- similarity due to convergent evolution (
  same function different structure) two kinds of
  moles

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Analogies
Marsupial
These moles only look similar
Placental
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Molecular Evidence

• Computers are used to analyze DNA sequences for
  homologous nucleic bases.

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Taxonomic Categories
Did (Domain) Karens (Kingdom) Pups (Phylum) Chew
(Class) On (Order) Fuzzy (Family) Grey
(Genus) Squirrels (Species)
?
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Binomial Nomenclature

• Example Escherichia coli, E. coli, Escherichia
  spp.,
• The genus name (Escherichia) is always
  capitalized and comes first
• The species name (coli) is never capitalized
• The species name is never used without the genus
  name
• The genus name may be used without the specific
  epithet
• Both genus and species names are always
  underlined or italicized
• Genera may be abbreviated, e.g., the E. in E.
  coli,

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Cladistics

• Cladistics is a technique by which organisms are
  assigned to different (monophyletic) taxa
• Cladistics works by grouping together organisms
  such that within taxa individuals share more
  homologies than they do with individuals found in
  different taxa
• Cladistics also rejects the inclusion of
  similarities...
• that result from convergent evolution (i.e.,
  analogies)
• that are homologies that are shared with other
  taxa (i.e., shared primitive characteristics)

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Classifying Clades
Each deeper branch point represents greater
divergence
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Classifying Proper Clades Passing the Test
A clade consists of an ancestral species plus all
descendant species
Here is a missed ancestor species
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Monophyletic
All descendants
A correct grouping
A clade
Ancestor
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Paraphyletic
This is missing descendant species
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Polyphyletic
Convergent evolution?
Polyphylies happen when species are included in
clades that they dont belong in
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Convergent Evolution

• Polyphyletic taxa occur as a consequence of
  mistaking analogies for homologies
• Analogies result from convergent evolution the
  two species do similar things in similar
  environments so evolve similarly
• The key difference between an analogy and a
  homology is
• The common ancestor between the two species will
  lack the common structure

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Analogies
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Shared Derived Characters SDC
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Cladogram based on Shared Derived Characteristics.
An outgroup is a species that is related to the
species being studied (ingroup), but less closely
related
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Molecular Clocks

• The molecular clock is a yardstick for measuring
  absolute time of evolutionary change based on the
  observation that some genes and other regions of
  genomes seem to evolve at constant rates

Neutral theory states that much evolutionary
change in genes and proteins has no effect on
fitness It states that the rate of molecular
change in these genes and proteins should be
regular like a clock
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Applying a Molecular Clock- The Origin of HIV

• Phylogenetic analysis shows that HIV is descended
  from viruses that infect chimpanzees and other
  primates
• Comparison of HIV samples throughout the epidemic
  shows that the virus evolved in a very clocklike
  way

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Universal Tree of Life

• The tree of life is divided into three great
  clades called domains Bacteria, Archaea, and
  Eukarya
• 1- last common ancestor of all living things
• 2. ancestor of eukaryotic cells
• 3. symbiosis of mitochondrial ancestor
• 4. symbiosis of chloroplast ancestor

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