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Chapter 25 Tracing Phylogeny

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Chapter 25 Tracing Phylogeny Linnaeus Taxonomy 1. Binomial Nomenclature two names for each organism. Ex - Homo sapiens 2. Hierarchical System arranges life ... – PowerPoint PPT presentation

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Title: Chapter 25 Tracing Phylogeny


1
Chapter 25Tracing Phylogeny
2
Phylogeny
  • Phylon tribe, geny genesis
    or origin
  • The evolutionary history of a species or a group
    of related species.

3
Phylogeny
  • Found in fossils and the fossil record.

4
Fossils
  • Any preserved remnant or impression of a past
    organism.

5
Types of Fossils
  • 1. Mineralized
  • 2. Organic Matter
  • 3. Trace
  • 4. Amber

6
Mineralized Fossils
  • Found in sedimentary rock.
  • Minerals replace cell contents.
  • Ex bone, teeth, shells

7
Organic Matter Fossils
  • Retain the original organic matter.
  • Ex plant leaves trapped in shale.
  • Comment can sometimes extract DNA from these
    fossils.

8
Trace Fossils
  • Footprints and other impressions. No organic
    matter present.

9
Amber
  • Fossil tree resin.
  • Preserve whole specimen.
  • Usually small insects etc.

10
Fossils - Limitations
  • Rare event.
  • Hard to find .
  • Fragmentary.
  • Dating.

11
Fossil Dating Methods
  • 1. Relative - by a fossil's position in the
    strata relative to index fossils.
  • 2. Absolute - approximate age on a scale of
    absolute time.

12
Absolute - Methods
  • 1. Radioactive
  • 2. Isomer Ratios

13
Radioactive
  • Estimated from half-life products in the fossil.
  • Ex Carbon - 14 Potassium - 40

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15
Isomer Ratios
  • Ratio of L- and D- amino acid isomers.
  • L- used by living things.
  • D- not used by living things.

16
Death
  • L- form ? D- form
  • Age can be calculated from the ratio of L-/D- as
    long as the temperature of the area is taken into
    account.

17
What do fossils tell us?
  • That the geographical distribution of organisms
    has changed over time.
  • Reason? The land formations of the earth have
    changed.

18
Continental Drift
  • The movement of the earth's crustal plates over
    time.
  • Drift is correlated with events of mass
    extinctions and adaptive radiations of life.

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21
Result of plate movement
  • Geographical Isolation.
  • New environments formed.
  • Old environments lost.
  • As the environments changed, so did Life.

22
Example
  • Australian fauna and flora are unique.
  • Separated early and remained isolated for 50
    million years.

23
Mass Extinctions
  • The sudden loss of many species in geologic time.
  • May be caused by asteroid hits or other disasters.

24
Examples
  • Permian Extinction
  • Cretaceous Extinction

25
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26
Permian Extinction
  • 250 million years ago.
  • 90 of species lost.

27
Cretaceous Extinction
  • 65 million years ago.
  • Loss of the dinosaurs.
  • Good evidence that this event was caused by an
    asteroid that hit in the Yucatan, causing a
    nuclear winter.

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29
The crater
30
Result of Mass Extinctions
  • Climate changes.
  • Areas are open for the surviving species to
    exploit.
  • Rapid period of speciation (adaptive radiation).
  • Many new species are formed in a very short
    period of time.

31
Systematics
  • The study of biological diversity.
  • Uses evidence from the fossil record and other
    sources to reconstruct phylogeny.

32
Systematics fuses
  • 1. Phylogeny- tracing of evolutionary
    relationships.
  • 2. Taxonomy- the identification and
    classification of species.

33
Taxonomy
  • Natural to humans.
  • Modern system developed by Linnaeus in the 18th
    century.

34
Linnaeus Taxonomy
  • 1. Binomial Nomenclature two names for each
    organism.
  • Ex - Homo sapiens
  • 2. Hierarchical System arranges life into
    groups. Ex -
    Kingdom ? Species

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36
Goal of Systematics
  • To have Taxonomy reflect the evolutionary
    affinities or phylogeny of the organisms.

37
Phylogenetic tree
38
Question?
  • How to group taxa so that the phylogenetic
    relationships are correct ?

39
Ideal Situation
  • Monophyletic Grouping - a single ancestor gave
    rise to all species in the taxon.

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41
Other Possibilities
  • Polyphyletic - grouping where members are derived
    from two or more ancestral forms.
  • Paraphyletic - grouping that does not include
    all members from an ancestral form.

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43
Problem
  • Not all likeness is inherited from a common
    ancestor.
  • Problem is of homology vs analogy.

44
Homology and Analogy
  • Homology likeness attributed to shared
    ancestry.
  • Ex forelimbs of vertebrates
  • Analogy likeness due to evolution solution for
    the same problem.
  • Ex wings of insects and birds

45
Convergent Evolution
  • When unrelated species have similar adaptations
    to a common environment. A specific example of
    Analogy.
  • Ex Sharks and dolphins

46
Only one is a cactus
47
Question
  • Can parallel evolution actually happen?

48
Need
  • Methods to group organisms by similarities and
    phylogenies.
  • One possible method is Molecular Systematics.

49
Molecular Systematics
  • Compares similarities at the molecular level.
  • Ex DNA, Proteins

50
DNA Comparisons
  • A direct measure of common inheritance.
  • The more DNA in common, the more closely related.

51
African Violets
  • 2 nuclear DNA and 2 chloroplast DNA studies found
    only 6 groups that clustered by mountain.
  • New collections found many intermediate forms
    between the former species.

52
New Taxonomy
  • Reorganized into 6 species and 10 subspecies.
  • African violets are in the process of splitting
    apart.

53
Schools of Taxonomy
  • 1. Phenetics Taxonomic affinities based on
    measurable similarities.
  • 2. Cladistics Branch points defined by novel
    characteristics.

54
Cladistics
55
Problem ?
56
Todays Systemics
  • Uses clues from evolution.
  • Balances Phenetics and Cladistics.

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58
Result
  • Taxonomy will become Genealogies, reflecting the
    organisms "Descent with
    Modification.

59
Summary
  • Recognize the use and limits of fossils.
  • What happens to evolution in mass extinctions.
  • What is phylogeny?

60
Summary
  • What is a phyletic tree?
  • How is molecular systematics used in phylogeny?
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