phylogenetic tree: visual representation of the ... · phylogenetic tree: visual representation of...

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