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Chapter 10

BIOC51H3 Chapter Notes - Chapter 10: Phylogenetic Tree, Synapomorphy

Biological Sciences
Course Code
Maydianne Andrade

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Chapter 10
10.4 - The comparative method
-The comparative method seeks to evaluate hypotheses by testing for patterns across species,
such as correlations among traits, or correlations between traits and features of the
-pattern shows as a bat species evolved larger roosting group sizes than its species -> also
evolved larger testes for body size
Chapter 4
-phylogeny: evolutionary history of a group of species
-phylogenetic tree: graphical summary of this history
4.1 - The Logic of Phylogeny Inference
-the most closesly related taxa should have the most traits in common
-synapomorphy: homologous trait that is shared amongst certain species and is similar b/c it was
modified in a common ancestor
-shared, derived trait
-monophyletic groups are comprised of an ancestor and all of its descendents
-e.g. all living organisms (shared genetic code)
-bacteria + mammals = same monophyletic group, but each have synapomorphies that
identify them as distinct monophyletic groups
-all synapomorphies are homologous traits, but not all homologous traits are synapomorphies
(can be identified @ all taxa levels)
-1. speciation: when 2 population become genetrically isolated (gene flow reduced, absent)
separation occurs, species begin evolving independently
-2. each branching event adds 1+ derived trait
-not all similar traits are homologous
-morphological similarities evolve independently in different lineages due to convergent
evolution: natural selection favours similar structures as solution similar to similar
environmental problems
-these similar traits are not homologous and dont qualify as synapomorphies (e.g. wings of
bats + birds, streamline shape of shark and whales..)
-reversals could happen @ molecular level for DNA (if so, the resultant similar traits are not
homologous and so does not qualify as synapomorphies)
-reversals and convergence = homoplasy (similarities NOT due to homology)
-To distinguish between homology and homoplasy is to analyze many traits in reconstructing
evolutionary relationships
-parsimony: a way to indentify which branching pattern minimizes the effects of homoplasy +
accurately reflect actual evolutionary history.
-prefer simple over complex.
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