ch. 26 phylogeny and the tree of life · 2011-01-03 · ch. 26 phylogeny and the tree of life. 2...
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Ch. 26Phylogeny and The Tree of Life
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Essential Question:
How do we relate the information of evolution to the classification of organisms?
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Phylogeny = the evolutionary history of a species or groups of species
Systematics = classifying organisms and determining their evolutionary relationships
molecular systematics looks at molecular sequences
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Classification Schemes
• Aristotle Plants and animals
• Carolus Linnaeus Binomial Nomenclature
genus & speciesEx. Homo sapiens = "wise man"
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• In 1969, R.H Whittaker argued for a fivekingdom system: Monera, Protista, Plantae, Fungi, and Animalia.
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• Three kingdoms of multicellular eukaryotes were distinguished by nutrition, in part.Plant are autotrophic, making organic food by photosynthesis.Most fungi are decomposers with extracellular digestion.Most animals digest food within specialized cavities.
• Protista consisted of all eukaryotes that did not fit the definition of plants, fungi, or animals.
• The fivekingdom system prevailed in biology for over 20 years.
• threedomain system: Bacteria, Archaea, and Eukarya, as superkingdoms.
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• taxonomy at the highest level is a work in progress.
• There will be much more research before there is anything close to a new consensus for how the three domains of life are related and how many kingdoms there are.
• New data will undoubtedly lead to further taxonomic modeling.
• Keep in mind that phylogenetic trees and taxonomic groupings are hypotheses that fit the best available data.
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Systematics = the study of biological diversity in an evolutionary context
includes taxonomy naming and classification of species and groups of species
Carolus Linnaeus father of binomial nomenclaturegenus, species Ex Homo sapiens
Hierarchical classification:DomainKingdomPhylumClass Order Family Genus Species
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taxon = taxonomic unit at any level
can make phylogenic trees (branching diagram of evolutionary history)
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Phylogenic systematics = classification based on evolutionary history
based on:a. fossil evidenceb. DNA evidence
Types:PhyloCode Classification only names groups that include
a common ancestor and all of its descendentsCladograms based on dichotomies
each branch is a clade all ancestral species and all of its descendents (monophyletic)
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Phylogenic trees what they do and do not tell us
1. doesn't indicate actual ages of a particular species
2. Cannot assume that a taxon on a tree evolved from the one next to it
3. Do allow scientists to can identify close relatives if have DNA data.
4. Used to tell strain of anthrax used in bioterrorism attacks
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Phylogenies can be inferred from morphological and molecular data
Ex. homologous structures
Problems come with analogous structures Ex. bats and birds bats more closely related to a cat than a bird
but have a common ancestor a tetrapod that couldn't fly
Homoplasies Analogous structures that arose independently
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Aligning segments of DNA
Evaluating Molecular Homologies
1. DNA segments are aligned
2. Deletion and insertion mutations shift sequences
3. two shaded regions do not align due to mutations
4. homologous regions realign after computer adds gaps in sequence 1
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Shared Characters to construct phylogenic trees
Cladistics An approach to systematics in which organisms are placed into groups called clades based on common descent
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Monophyletic vs. paraphyletic vs. polyphyletic
monophyletic consists of an ancestral species and all its descendentsParaphyletic consists of an ancestral species and some, but not all, of its descendentsPolyphyletic inclueds taxa with different ancestors
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How cladograms are made
a.look at homologyexception can't look at convergent evolution species (species from different evolutionary branches that resemble each other due to similar ecological roles and
natural selection have analogous adaptations)
the greater homology between species the closer related they tend to be
the more comlex two similar structures are, the less likely they evolved separately
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convergent evolution and analogous structures
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b. shared derived characters (feature of a particular taxon)shared primitive character a character that originated in an ancestor of the taxon
Ex. vertebral columnshared derived character novelty unique to a particular clade
Ex. Hair of mammal
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c. using an outgroup (species or group of species from an evolutionary lineage that is known to have diverged before the lineage that includes the species being studied an ingroup)
cladograms show relationships, not necessarily chronologic data
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Branch lengths can indicate relative amounts of genetic change
Above phylogenic tree represents compared sequences of a homologous gene that plays a role in development
Branch lengths = amount of genetic change
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d. use Parsimony "nature should be simple" smallest number of evolutionary changes
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Maximum Parisimony A principle that states that when considering multiple explanations for an observation, one should first investigate the simplest explanation that is consistent with the facts.
ex. in trees based on morphology the most parsiminous tree requires the fewest evolutionary events
Ex. for DNA based trees the most parsiminous tree requires the fewest base changes
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Maximum Likelihood principle when considering multiple phylogenic hypotheses, one should take into account the hypothesis that reflects the most likely sequence of evolutionary events, given certain rules about how DNA changes over time.
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An organism's evolutionary history is documented in its genome
different genes evolve at different ratesEx. can use mitochondrial DNA to look at recent evolutionary events because it evolves relatively rapidly.
orthologous genes homlogous genes that are found in different species because of speciation
Ex. Cytochrome c in ETC in humans and dogsparalogous genes result from gene duplication found as more than one copy in genome
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Molecular clocks can be used to relate taxonomic groups
are timing methods based on observation that at least some regions of genomes evolve at constant rates
ex. # of nucleotide and amino acid substitutions is proportional to the time that has elapsed since the lineages branched
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Has been used to date when HIV1 M invaded humans from primates (1930's)
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Modern systematics is shaking some phylogenic trees
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Three domains based on rRNA gene sequences