Transcript Chapter 25: Phylogeny & Systematics

Chapter 25: Phylogeny &
Systematics
Phylogeny
Evolutionary history of species or group of
species
**Attempting to construct the universal
tree of life
Information contributing to
Phylogenics
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Fossil record
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Substantial but incomplete & biased chronicle
of evolutionary change
Systematics
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analytical approach to understanding the
diversity & relationships of present day &
extinct organisms through morphological &
biochemical resemblances
Systematics
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Morphological homologies
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Molecular homologies
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Similar bone structures indicate species share
a common ancestor
Similarities in DNA, RNA, & other molecules
indicate species share a common ancestor
**Potential problems for phylogeny
Analogous structures (homoplasies) &
convergent evolution
Taxonomy
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Ordered division of organisms into
categories based on a set of
characteristics used to assess similarities &
differences
Useful for phylogenic systematics
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Binomial designations (Genus species)
Hierarchical classifications
Phylogenetic Trees
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Depict hypothesis about evolutionary
relationships of a species in relative periods of
time
Cladistics
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Analysis of how species may be grouped into clades
distinguishing analogous from homologous structures
Cladogram
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Depicts patterns of shared characteristics, not necessarily
evolutionary history
Can be converted to phylogenetic trees with support from
fossils, biochemistry, etc.
Clade
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Group of species in the phylogenetic tree that includes an
ancestral species & all its descendants
Phylogenetic Trees
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Monophyletic
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Paraphyletic
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Clade consists of ancestral species & its
descendants
Grouping in which information is missing on
some members of the clade
Polyphyletic
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Grouping of several species that lack a
common ancestor
Preparing phylogenetic trees
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Ingroup
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Outgroup
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Novelty trait of a clade
Maximum parsimony
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Trait shared beyond the taxon being defined
Shared derived character
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Species or group of species closely related to ingroup
Used to differentiate shared derived & shared primitive
characteristics
Shared primitive character
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Species being studied
Fewest number of evolutionary events occur to reach form of
shared derived characteristics
**Nature doesn’t always follow easiest course ex. 4 chamber
heart
Maximum liklihood
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Incorporate as much information as possible to reflect the most
likely sequence of evolutionary events
Evolutionary Diagrams depicting
time
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Phylogram
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Present information about the sequence of
events relative to each other
Branch length=# changes in DNA sequence
which have occurred in that lineage
Ultrametric trees
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Show sequence of evolutionary events in
context of geologic time
Molecular Clocks
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Measures absolute time of evolutionary change
based on observations that some genes & other
regions of genomes evolve at constant rates
DNA coding for rRNA changes relatively slowlyused to study relationships of distantly related
species
DNA in mitochondria (mtDNA) evolves rapidly –
used to study recently diverged species
Orthologous genes
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Homologous genes passed from one generation to
the next but end up in different gene pools as a result
of speciation
Ex. Beta globin genes in humans & mice
Paralogous genes
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Result from gene duplication in one genome
Ex. Olfactory genes
Universal Tree of Life
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Tree consists of 3 great domains
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Bacteria
Archaea
Eukarya
Early history of the domains is not yet
clear
Molecular systemactics & clocks used to
construct