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Phylogeny and the Tree of Life

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Chapter 26 Phylogeny and the Tree of Life – PowerPoint PPT presentation

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Title: Phylogeny and the Tree of Life


1
Chapter 26
  • Phylogeny and the Tree of Life

2
Investigating the Tree of Life
  • Phylogeny is the evolutionary history of a
    species or group of related species
  • Phylogenies have two components
  • branching order (showing group relationships)
  • branch length (showing amount of evolution). 
  • The discipline of systematics classifies
    organisms and determines their evolutionary
    relationships
  • Systematists use fossil, molecular, and genetic
    data to infer evolutionary relationships

3
Linnaeus Contribution
  • Taxonomy is the ordered division and naming of
    organisms
  • In the 18th century, Carolus Linnaeus published a
    system of taxonomy based on resemblances
  • Two key features of his system remain useful
    today two-part names for species and
    hierarchical classification

4
  • The two-part scientific name of a species is
    called a binomial
  • The first part of the name is the genus
  • The second part, the specific epithet, is unique
    for each species within the genus
  • Capitalize the first letter of genus name only
    and write in italics or underline
  • Example Homo sapiens Acer rubrum
  • (modern humans) (red
    maple tree)

5
Hierarchical Classification
  • Linnaeus introduced a system for grouping species
    in increasingly broad categories
  • The taxonomic groups from broad to narrow are
    domain, kingdom, phylum, class, order, family,
    genus, and species
  • A taxonomic unit at any level of hierarchy is
    called a taxon

6
Fig. 26-3
Species Panthera pardus
Genus Panthera
Family Felidae
Order Carnivora
Class Mammalia
Phylum Chordata
Kingdom Animalia
Archaea
Domain Eukarya
Bacteria
7
Linking Classification and Phylogeny
  • Linnaean classification uses a pyramid-type
    diagram to depict linneage
  • Systematists depict evolutionary relationships in
    branching phylogenetic trees

8
Fig. 26-4
Species
Order
Family
Genus
Pantherapardus
Panthera
Felidae
Taxidea taxus
Taxidea
Carnivora
Mustelidae
Lutra lutra
Lutra
Canis latrans
Canidae
Canis
Canis lupus
9
Fig. 26-5
Branch point (node)
Taxon A
Taxon B
Sister taxa
Taxon C
ANCESTRAL LINEAGE
Taxon D
Taxon E
Taxon F
Common ancestor of taxa AF
Polytomy more than 2 groups emerge
10
What We Can and Cannot Learn from Phylogenetic
Trees
  • Phylogenetic trees do show patterns of descent
  • Phylogenetic trees do not indicate when species
    evolved or how much genetic change occurred in a
    lineage
  • It shouldnt be assumed that a taxon evolved from
    the taxon next to it

11
Homology and Analogy
  • Homology is similarity due to shared ancestry
    like between a wolf and a coyote
  • Analogy is similarity due to convergent
    evolution, similar conditions/adaptations

Australian "mole"
Look alike, but evolved independantly from
each other
North American mole
12
  • Analogies are also known as homoplasies ("to mold
    the same way")
  • Homology can be distinguished from analogy by
    comparing fossil evidence and the degree of
    complexity
  • The more complex two similar structures are, the
    more likely it is that they are homologous
  • Systematists use computer programs and
    mathematical tools when analyzing comparable DNA
    segments from different organisms

13
Fig. 26-8
1
Deletion
2
Types of mutations that normally occur
Insertion
3
Orange sections no longer align
4
only with addition of gaps will they align
14
  • It is also important to distinguish homology from
    analogy in molecular similarities
  • Mathematical tools help to identify molecular
    homoplasies, or coincidences
  • Molecular systematics uses DNA and other
    molecular data to determine evolutionary
    relationships

15
Constructing phylogenetic trees
  • Cladistics groups organisms by common descent
  • A clade is a group of species that includes an
    ancestral species and all its descendants
  • A valid clade is monophyletic, signifying that it
    consists of the ancestor species and all its
    descendants
  • A paraphyletic grouping consists of an ancestral
    species and some, but not all, of the descendants
  • A polyphyletic grouping consists of various
    species that lack a common ancestor

16
Fig. 26-10
Includes all descendants
A
A
A
Group I
B
B
B
C
C
C
D
D
D
Group III
Group II
E
E
E
F
F
F
G
G
G
(b) Paraphyletic group
(a) Monophyletic group (clade)
(c) Polyphyletic group
17
Shared Ancestral and Shared Derived Characters
  • In comparison with its ancestor, an organism has
    both shared and different characteristics
  • A shared ancestral character is a character that
    originated in an ancestor of the taxon
  • A shared derived character is an evolutionary
    novelty unique to a particular clade
  • A character can be both ancestral and derived,
    depending on the context, it is useful to know in
    which clade a shared derived character first
    appeared

18
Fig. 26-11
TAXA
Lancelet (outgroup)
Lancelet (outgroup)
Salamander
Lamprey
Lamprey
Leopard
Turtle
Tuna
Tuna
Vertebral column (backbone)
0
1
1
1
1
1
Vertebral column
Hinged jaws
0
0
1
1
1
1
Salamander
Hinged jaws
CHARACTERS
1
0
0
0
1
1
Four walking legs
Turtle
Four walking legs
0
0
0
0
1
1
Amniotic (shelled) egg
Amniotic egg
Leopard
Hair
0
0
0
0
0
1
Hair
(a) Character table
(b) Phylogenetic tree
19
  • An outgroup is a species or group of species that
    is closely related to the ingroup, the various
    species being studied
  • Systematists compare each ingroup species with
    the outgroup to differentiate between shared
    derived and shared ancestral characteristics
  • Homologies shared by the outgroup and ingroup are
    ancestral characters that predate the divergence
    of both groups from a common ancestor
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