Transcript Phylogeny and Systematics

Phylogeny and
Systematics
The Tree of Life
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Phylogeny is the evolutionary history of a
species (or group of species)
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To determine phylogeny, evolutionary biologists use:
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The fossil record
Systematics
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An analytical approach to understanding relationships between
organisms
Traditionally have used morphological and biochemical
resemblances (homologous structures, etc.)
***Molecular systematics –
 Compares DNA and RNA to infer evolutionary relationships
The Fossil Record
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The fossil record is based
on the sequences in which
fossils have accumulated in
strata of rocks
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Relative vs. absolute dating
The fossil record is an
important but incomplete
chronicle of evolutionary
change
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Only organisms with hard
parts (ie. skeleton) could be
preserved as fossils
Many fossils have not been
discovered
Morphological and Molecular
Homologies
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In general, organisms
that share very similar
morphologies (forms) or
similar DNA sequences
are more likely to be
closely related
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Homologous structures
 Examples:
Convergent Evolution
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HOWEVER, convergent evolution occurs
when similar environmental pressures and
natural selection produce similar
(analogous) adaptations in organisms from
different evolutionary lineages
 In other words, the SAME PRESSURES
cause the SAME adaptations to evolve
INDEPENDENTLY
 Example:
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Bats and birds have adaptations that allow
them to fly
This might imply that bats and birds are
closely related, perhaps more closely
related than bats and mammals. NOT
TRUE!
Bat’s forelimb is homologous to other
mammals, but analogous to a bird’s wing
Homologous vs. Analogous
Structures
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Homologous Structures –
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Similar anatomical structures that came from a common ancestor
as a result of divergent evolution
Analogous Structures –
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Anatomical structures that are similar and perform the
same/similar function but evolved SEPARATELY
A result of convergent evolution
Taxonomy
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Taxonomy is the ordered
division of organisms into
categories based on similar
characteristics
Carolus Linnaeus began
taxonomy in the 18th century
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However, his system of
taxonomy is under some attack
now because his classification
was based on resemblances,
NOT evolutionary relationships
Linnean Classification
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Binomial Nomenclature:
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2-part format of the
scientific name
Genus and species
Hierarchical Classification
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Linnaeus grouped species
into a hierarchy of
increasingly broad
categories
Genus – Family – Order – Class – Phylum – Kingdom – Domain
Apt. - Apt. Bldg. – Street – City – State - Country - Continent
Phylogenetic Trees
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Phylogenetic trees are
branching diagrams that
show hypotheses about
evolutionary relationships
between organisms
REMINDER:
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Phylogenetic trees
represent HYPOTHESES
about how organisms are
related
A good hypothesis must be
revised when new data is
revealed
Cladograms
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Cladograms show
patterns of shared
characteristics and
can help us infer
evolutionary
relationships (as long
as they’re due ONLY to
homology, NOT
analogy)