Chapter 26 Phylogeny and the Tree of Life

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Chapter 26Phylogeny and the Tree of Life

• Professor Pamela L. Pannozzo
• Principles of Biology II BSC 1011

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How Do We Trace and Organize Evolutionary
Relationships?

• Phylogeny the evolutionary history of a species
  or group of species
• Systematics study of classifying organisms
  based on evolutionary relationships
• Taxonomy study of naming and classifying
  organisms

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Classification

• Binomial nomenclature
• Homo sapiens
• Linnaean system of classification

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Phylogenetic Trees
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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
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Ways We Determine Phylogenies

• Morphological similarities
• Homologous vs. analogous structures
• Molecular homologies

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Divergent Evolution

• The evolution of different species from a common
  ancestor

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Convergent Evolution

• The evolution of similar features in independent
  evolutionary lineages

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Similar DNA Sequences

• Align comparable sequences
• Analyze for insertions and deletions
• Percentage of DNA differences correlated with
  evolutionary relatedness

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Cladistics

• Monophyletic group an ancestral specia and all
  of its descendants
• Paraphyletic group an ancestral species and
  some of its descendants
• Polyphyletic group two or more ancestral
  species and their descendants

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Phylogenetic Trees are Constructed Based on
Shared Characteristics
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Evolutionary History of Documented in Genomes

• Different genes evolve at different rates
• Allows comparisons of genomes of different
  organisms
• 50 human and yeast genes orthologous
• 99 human and mice genes orthologous
• Number of genes not correlated with phenotypic
  complexity

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Molecular Clocks

• Graph of the number of mutations that have
  occurred in a gene over time
• Assumption that some genes evolve at constant
  rates
• Number of base substitutions between two genes is
  proportional to time elapsed since divergence
  from common ancestor
• Can use nucleotides, codons, or amino acids

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Molecular Clocks
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Current Domains Classification
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Tree of Life Based on rRNA
? major horizontal gene transfer