Lec6_Phylo - THINK TREES! Phylogenetics The science of...

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1 Phylogenetics The science of reconstructing trees THINK TREES! E=mc 2 3 Cladistics: Only certain types of homologous characters are useful for inferring trees: Synapomorphies (shared derived characters) 4 Cladistics: Only certain types of homologous characters are useful for inferring trees: Synapomorphies (shared derived characters)
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5 How to tell if a character is derived or ancestral? The OUTGROUP COMPARISON out ingroup 6 How to tell if a character is derived or ancestral? The OUTGROUP COMPARISON Choose an OUTGROUP known (on the basis of other evidence) to be OUTSIDE the group of interest Character states present in the outgroup are assumed to be ancestral Character states present only in the ingroup are potentially synapomorphies out ingroup 7 8 Determine the phylogenetic relationships among turtles, crocodiles, birds, and lizards. Use amphibians as an outgroup Attention! Do not memorize characters. Understand the principle!
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Character Birds Crocs Lizards Turtles Frog Feathers + - - - - Amniotic egg + + + + - Parental care + + - - - Four chambered heart + + - - - Outer carapace - - - + - Two skull fenestra + + + - - Absent(-) vs Present(+) To reconstruct a tree we need characters. But not any old character! We need: Homologous characters and synapomorphies ! 1 0 Character Birds Crocs Lizards Turtles Frog Feathers + - - - - Amniotic egg + + + + - Parental care + + - - - Four chambered heart + + - - - Outer carapace - - - + - Two skull fenestra + + + - - Absent(-) vs Present(+) To reconstruct a tree we need characters. But not any old character! We need: Homologous characters and synapomorphies ! 1 1 Cladistic estimation of phylogeny (with informative characters shown) Amniotic egg: present Heart chambers: four Parental care: present Skull fenestra: two 1 2 Cladistic estimation of phylogeny (with informative characters shown)
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Lec6_Phylo - THINK TREES! Phylogenetics The science of...

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