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Chapter 25: Phylogeny and Systematics

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Chapter 25: Phylogeny and Systematics Fossils are preserved remnants of organisms that lived in the past Fossils form in sedimentary rock, the oldest fossils in the ... – PowerPoint PPT presentation

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Title: Chapter 25: Phylogeny and Systematics


1
Chapter 25 Phylogeny and Systematics
2
Taxonomy is the division of organisms into
categories based on similarities and
differences. p. 495, Campbell Reece (2005)
Shown is a phylogenetic tree
3

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.

4
Fossils
5
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

6
Analogies
Marsupial
These moles only look similar
Placental
7
Molecular Evidence
  • Computers are used to analyze DNA sequences for
    homologous nucleic bases.

8
Taxonomic Categories
Did (Domain) Karens (Kingdom) Pups (Phylum) Chew
(Class) On (Order) Fuzzy (Family) Grey
(Genus) Squirrels (Species)
?
9
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,

10
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)

11
Classifying Clades
Each deeper branch point represents greater
divergence
12
Classifying Proper Clades Passing the Test
A clade consists of an ancestral species plus all
descendant species
Here is a missed ancestor species
13
Monophyletic
All descendants
A correct grouping
A clade
Ancestor
14
Paraphyletic
This is missing descendant species
15
Polyphyletic
Convergent evolution?
Polyphylies happen when species are included in
clades that they dont belong in
16
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

17
Analogies
18
Shared Derived Characters SDC
19
Cladogram based on Shared Derived Characteristics.
An outgroup is a species that is related to the
species being studied (ingroup), but less closely
related
20
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
21
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

22
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

23
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