BIOC51H3 Chapter Notes - Chapter 10: Phylogenetic Tree, Synapomorphy

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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
environment.
-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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Document Summary

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 environment. Pattern shows as a bat species evolved larger roosting group sizes than its species -> also evolved larger testes for body size. Phylogeny: evolutionary history of a group of species. Phylogenetic tree: graphical summary of this history. 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 modi ed in a common ancestor. 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 identi ed @ all taxa levels)

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