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BIOLOGY 171

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Title: BIOLOGY 171


1
BIOLOGY 171
CHAPTER 25 Phylogeny and Systematics
2
Investigating the Tree of Life
  • Phylogeny Evolutionary history of a species
  • Systematics Study of the diversity and
    relationships of life.
  • Molecular Systematics Use of DNA, RNA and other
    molecular evidence to infer evolutionary
    relationships between genes and genomes.

3
HOW FOSSILS FORM
  • Most fossils are formed in sedimentary rock.
  • Most fossils result from preservation of hard
    rather than soft parts.
  • Some fossils result from petrification

4
HOW FOSSILS FORM
  • TYPES OF FOSSILS
  • Thin organic layers sandwiched between layers
    of rock.
  • Molds and prints
  • Trace fossils are footprints, burrows, etc.
  • Entire organism is preserved.
  • Anaerobic environments that prevent decay.
    (amber)

5
AMBER
FOSSIL TYPES
MOLDS / PRINTS
HARD PARTS
6
TRACE
FOSSIL TYPES
PETRIFICATION
ORGANIC LAYER
7
LIMITATIONS OF THE FOSSIL RECORD
  • All fossils are accidents of an unusual
    sequence of events.
  • Many types of organisms or body parts are not
    easily fossilized.
  • Only a small fraction of organisms to have
    lived produce fossils.
  • An even smaller fraction of fossils are
    discovered.

8
Morphological and Molecular Homologies
  • Morphological homologies
  • Molecular homologies
  • Homology vs. Analogy
  • Homoplasies
  • Evaluating Molecular Homologies

9
Evaluating Molecular Homologies
10
MOLECULAR BIOLOGY AND SYSTEMATICS
  • A. Protein Comparison
  • B. DNA Comparison
  • DNA-DNA Hybridization
  • Restriction Mapping
  • DNA Sequencing
  • C. Analysis of Fossilized DNA
  • D. Molecular Clocks

11
CONVERGENT EVOLUTION
12
CLASSIFICATION AN OVERVIEW
  • EARLY HISTORY
  • THEOPHRASTUS
  • DE MATERIA MEDICA
  • HERBALS - DOCTRINE OF SIGNATURE
  • 17TH AND 18TH CENTURY - CLASSIFICATION
  • CARLOLUS LINNAEUS
  • BINOMIAL NOMENCLATURE
  • Systema naturae
  • GENUS AND SPECIFIC EPITHET

13
TERMINOLOGY OF SYSTEMATICS
  • Phylogeny
  • Taxonomy
  • Classification
  • Taxon
  • Hierarchy Of Classification
  • DOMAIN, KINGDOM, DIVISION, CLASS, ORDER, FAMILY,
    GENUS, SPECIES
  • Phylogenetic Trees

14
Taxonomic Hierarchy
15
Phylogenetic Systematics
  • Cladogram Diagram illustrating patterns of
    shared characteristics. If shared
    characteristics are homologies then the cladogram
    forms the basis of a phylogenetic tree.
  • Clade Ancestral species and all its
    descendants.
  • Cladistics Pattern of systematics in which
    species are grouped into clades.

16
CLADOGRAM
17
Cladogram
18
Cladistics
  • A true clade is a group with a single common
    ancestor.
  • Monophyletic single tribe/single common
    ancestor.
  • Paraphyletic A grouping with a single common
    ancestor but not all descendents.
  • Polyphyletic A grouping that lacks a single
    common ancestor.

19
Cladistics
20
Other Cladistic Factors
  • Shared Primitive Character A characteristic
    that shared beyond the clade under study.
  • Shared Derived Characteristic Evolutionary
    novelty unique to a particular clade.
  • Ingroup Group of related species under study.
  • Outgroup A species or group so species that are
    closely related to, but are outside the ingroup.

21
Building a Cladogram
22
Phylogenetic Trees and Timing
  • Phylograms Length of branches reflect the
    number of changes that have occurred to a
    particular DNA sequence in that lineage.
  • Ultrametric Trees The pattern is the same as a
    phylogram, but all branches traced to a common
    ancestor are the same length. Illustrates
    survival period for the lineage rather than the
    number of DNA changes.

23
Phylograms and Ultrametric Trees
Phylograms
Ultrametric Trees
24
Criteria for Construction of a Phylogenetic Tree
  • Maximum Parsimony Based on the fewest
    evolutionary events to have occurred as shared
    derived characteristics.
  • Parsimony Simplest explanation
  • Occams Razor
  • Maximum Likelihood With certain rules about DNA
    changes, over time a tree can be found that
    reflects the most likely sequence of evolutionary
    events.

25
Maximum Parsimony
26
Maximum Likelihood
27
Genetic Factors for Change
  • Phylogenetic Trees as Hypotheses
  • Gene Duplication and Gene Families
  • Orthologous Genes Homologous genes passed in a
    straight line.
  • Paralogous Genes Duplicated genes found in more
    than copy in thesame genome.
  • Genome Evolution

28
Phylogenetic Hypotheses
29
Orthologous and Paralogous Genes
30
Tree of Life
31
Molecular Clocks
  • Based on measuring the absolute time of
    evolutionary change based on the observation that
    some genes or regions of the genome evolve at a
    constant rate.
  • Neutral Theory
  • Difficulties with Molecular Clocks

32
FOSSIL DATING
  • Relative Dating
  • Sedimentation Rates
  • Absolute Dating
  • C-14 or U-238
  • C-14 has a half-life of 5,600 years.
  • The half-life of U-238 is 4.5 billion years.
  • Racemization

33
CARBON 14 DATING
34
CARBON 14 DATING
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