Ch. 26 – Phylogeny and the Tree Ch. 26 – Phylogeny and the Tree of Life of Life We can decide in which container to place a species by comparing its traits with those of potential close relatives We will survey the diversity and describe hypotheses regarding how it evolved Phylogeny Systematics • Discipline focused on classifying organisms and determining their evolutionary relationships (phylogeny)
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Ch. 26 – Phylogeny and the Tree of Life We can decide in which container to place a species by comparing its traits with those of potential close relatives.
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Ch. 26 – Phylogeny and the Tree of LifeCh. 26 – Phylogeny and the Tree of Life
We can decide in which container to place a species by comparing its traits with those of potential close relatives
We will survey the diversity and describe hypotheses regarding how it evolved
Phylogeny
Systematics• Discipline focused on classifying
organisms and determining their evolutionary relationships (phylogeny)
Phylogeny and SystematicsPhylogeny and Systematics
Taxonomy• Science of classification• Sort and identify
closely related species• Specific group is a
taxonBinomial nomenclature• 2 part Latin name• Genus, species
Phylogeny and SystematicsPhylogeny and Systematics• Hierarchical classification• Linnaeus’ 7 level scheme:
– Kingdom– Phylum (Division for plants and
fungi)– Class– Order– Family– Genus – Species
• Domains are now above kingdoms– 3 exist
• Taxon– Toxonomic unit at any level of
the hierarchy
Linking Classification and PhylogenyLinking Classification and PhylogenyPhylogenetic Tree• Diagram that displays
evolutionary relationships• The sequence of branching
symbolizes historical chronology.– The last ancestor common to both the
cat and dog families lived longer ago than the last common ancestor shared by leopards and domestic cats.
PhyloCode• Resulted due to difficulties with
the Linnean system• Only names groups that include a
common ancestor of all its descendents
• Ranks would no longer exist
Linking Classification and PhylogenyLinking Classification and PhylogenyReading a phylogenetic tree• Branch points
– Divergence• Sister taxa
– Groups of organisms that share an immediate common ancestor
• Rooted– Represents most common
ancestor of all taxa in the tree
• Basal Taxon– Lineage that diverges early
in the history of a group• Polytomy
– Branch point from which more than two descendent groups emerge
Phylogenetic TreesPhylogenetic Trees1. Intended to show
patterns of descent
2. Sequence of branching in a tree does not necessarily indicate the actual (absolute) ages of the particular species
3. Don’t assume that a taxon evolved from the taxon next to it
• Analyzing the taxonomic distribution of homologies enables us to identify the sequence in which derived characters evolved during vertebrate phylogeny.
Fig. 25.11
Construct a cladogram based on the following traits (characters) in the character table
Fig. 25.11
Morphological & Molecular HomologiesMorphological & Molecular HomologiesHomology• shared ancestry; causes likeness• Can vary in appearance but still not
in the genesAnalogy• convergent evolution• acquisition of similar characteristics
due to sharing similar ecological roles
• External appearance very similar but internal anatomy, physiology, and reproductive systems are dissimilar
• Homoplasies– Analagous structures that arise
independently
Molecular Molecular HomologiesHomologies
Comparisons of DNA
Molecular Systematics
• Uses data from DNA and other molecules to determine evolutionary relationships
CladisticsCladisticsCommon ancestry is the primary criterion used to classify
organismsClades• Groups that include an ancestral species and all of its
descendentsMonophyletic groupParaphyletic groupPolyphyletic group
CladisticsCladisticsMonophyletic group• Allows a taxon to be equivalent to a clade• Group of taxa that consists of an ancestor and all of its
descendentsParaphyletic group• Ancestral species and SOME of its descendentsPolyphyletic group• Taxa with 2 or more different ancestors
Shared Ancestral Character• Originated in an ancestor of the taxon• Backbone of mammalsShared Derived Character• Evolutionary novelty unique to a clade• Hair in mammals
Inferring Phylogenies using Derived CharactersInferring Phylogenies using Derived CharactersOutgroup• A species or group of species from an evolutionary lineage that is known
to have diverged before the lineage that includes the species we are studying (ingroup)
Evidence used for cladistics• Fossil record• Homology (morphology, embryology, reproduction)• DNA sequences• Biogeography• Direct observation
Gene Duplications & Gene FamiliesGene Duplications & Gene FamiliesTwo distinct types of homologous genesOrthologous genes• Found in different species and their
divergences traces back to the speciation events that produced the species
Paralogous genes• Multiple copies of genes have diverged from
one another in a species
Molecular ClocksMolecular ClocksMolecular Clock• A yardstick for measuring
the absolute time of evolutionary change based on the observation that some genes and other regions of genomes appear to evolve at constant rates
Neutral Theory• Most evolutionary change
has no effect on fitness
From Two Kingdoms to Three DomainsFrom Two Kingdoms to Three DomainsTwo Kingdoms• Plants and Animals Five Kingdoms• Monera, Protista, Plantae,
Fungi, Animalia• Prokaryotic v. Eukaryotic• Unicellular v. Multicellular• Autotrophic v.
Heterotrophic• How does each kingdom
classify?
From Two Kingdoms to Three DomainsFrom Two Kingdoms to Three DomainsThree Domains• Archaea• Bacteria• EukaryaSix-Kingdom system Eubacteria and
Archaebacteria Extreme
halophiles Thermoacidophil
es Methanogens
Alternatives to the 6 Kingdom SystemAlternatives to the 6 Kingdom SystemEight-Kingdom system -
proposed Protists split into 3
kingdoms Fungal like, plant
like, animal like
Still debate over splitting Archae and Eubacteria even further
Evolutionary history of organisms• Base on principle of parsimony (simplest explanation
is the best)Mechanisms of speciation• Geographic (allopatric speciation)• Sympatric speciation• Reproductive isolation by prezygotic barriers• Reproductive isolation by postzygotic barriersInvestigating phylogeny (evidence, strengths,