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Lecture 21-Phylogeny II.docx

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Western University
Biology 1001A
Beth Mac Dougall- Shackleton

Lecture 21- Phylogeny II  To understand patterns of relatedness, reconstruction of CA must be done  Outgroup analysis provides clues to which traits derived, which ancestral o Outgroup is a close relative of the species in question but it does not belong to the group o Evolution does not always proceed toward greater complexity  Reading and building phylogenies o Related to =/= descended from o More complex =/= more evolved  Not all simlilarites are homolougous  Not all homologies are synapomophies ( shared and derived states)  Is a trait ancestral or derived o Ancestral if it is present in outgroup and all ingroups o Ancestral if present in outgroup and SOME ingroups o Derived if absent in outgroup but present in SOME ingroups o ? if present in outgroup but none in ingroup  Cant tell if it was derived after CA or if it ancestral but lost in evolution o ? if absent in outgroup but present in all ingroups  The reasoning relies on parsimony o The simplest explanation is usually the best o Whichever tree requires the smallest number of evolutionary changes (gains or loses of a trait) is probably correct o Parsimony often used to evaluate potential phylogenetic series  How many potential trees are there o There are infinite number of potential phylogenetic series  Least evolution
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