phylogenetic tree: visual representation of the ... · phylogenetic tree: visual representation of...
TRANSCRIPT
Phylogenetic tree: visual representation of the
hypothesized evolutionary relationships between different
species or groups over time
Phylogenetic Tree Components
◼ Nodes (branch points): represent common ancestors
Phylogenetic Tree Components
◼ Branches: represent the relationship between nodes/species
Phylogenetic Tree Components
◼ Branches: represent the relationship between nodes/species
◆ Note: truncated branches represent extinctions
Further reading: https://www.khanacademy.org/science/high-school-biology/hs-
evolution/hs-phylogeny/a/phylogenetic-trees
Phylogenetic Tree Components
◼ Nodes (branch points): represent common ancestors
◼ Branches: represent the relationship between nodes/species
◼ Derived traits: traits different from the ancestor of the group or
species; mapped directly onto branches
Timenode
branch
derived
trait
Phylogenetic Tree Components
Practice:
1) For C and E:
a) Where is their common ancestor?
b) What traits do they share? What trait(s) differentiate them?
2) Are whiskers in B and E homologous or analogous?
Phylogenetic Tree Components
◼ Derived traits: traits different from the ancestor of the group or
species; mapped directly onto branches
◼ Clade (monophyletic group): group of species including one
ancestor and all its descendants
Time
Phylogenetic Tree Components
◼ Derived traits: traits different from the ancestor of the group or
species; mapped directly onto branches
◼ Clade (monophyletic group): group of species including one
ancestor and all its descendants
The “one-snip” rule
Phylogenetic Tree Components
Practice:
1) What clades can you form that include C?
2) Do C and D make a monophyletic group? Why or why not?
Cladogram Activity
◼ Steps:
◆ Brainstorm important traits
◆ Make data table
◆ Make tree, adding one trait at a time
◼ Can you come up with a different tree?
◼ Which tree is most parsimonious?
Ingroup and Outgroup◼ Ingroup: clade of interest
◼ Outgroup: “group of
organisms not belonging to
the group whose
evolutionary relationships
are being investigated” (Wikipedia)
Bigfoot (new species of manlike ape) or man in a
costume?
Parsimony (Occam’s razor)
Parsimony (Occam’s razor)
◼ The simplest
explanation is most
likely to be correct…
◼ Unless evidence is given
otherwise
Parsimony (Occam’s razor)
◼ Most parsimonious tree
◆ Has fewest appearances or disappearances of
traits
◆ Most probable
Parsimony (Occam’s razor)
◼ The more traits you map, the more certain you can
be that your tree is accurate.
◆ Modern genetic analysis→ unlimited traits!
Vocabulary so far
◼ Phylogenetic tree
◼ Node
◼ Branch
◼ Common ancestor
◼ Homologous trait
◼ Analogous trait
◼ Derived trait
◼ Clade (monophyletic group)
◼ Ingroup
◼ Outgroup
◼ Parsimony