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Lecture 1

Biology 1201A Lecture Notes - Lecture 1: Phylogenetic Tree, Common Descent, Phylogenetics

Course Code
BIOL 1201A
Jennifer Waugh

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Lecture #1
Interpreting Phylogenies (or Phylogenetic Trees):
Phylogenetic trees are a hypothesis of the evolutionary relationship among various taxa,
Common ancestry
Modern or currently alive (extant) and extinct taxa
-If a branch stops, and doesn’t make it to the end, it represents an extinct taxa
Sequence of events
Relative relatedness of taxa
Interpreting Phylogenies:
Do these three phylogenies show the same evolutionary relationship among species? If they
differ, which ones differ?
1 and 2 are the same
3 is unique
Creating a phylogenetic tree:
Collect taxa in increasingly inclusive groups
Start with a exclusive group then slowly add more and more characteristics that
include more and more diverse individuals
Monophyletic Groups: include all taxa that descend from a common ancestor
Non-monophyletic Groups:
Anything that doesn’t meet the description of monophyletic groups
Only some taxa form a common ancestor
Taxa from diverse linages
Identify related taxa by similarity of traits
Closely related taxa should have traits in common
Homologies: traits shared by taxa due to inheritance from a common ancestor
Homoplasies: similarities not due to a common ancestor
Potentially a result of convergent evolution
Apparent differences/dissimilarity due to differing selection pressures
Misleadingly makes taxa appear unrelated despite a recent common ancestor
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