I.
A.
II.
PHYLOGENY AND THE TREE OF LIFE
CH 26
Phylogeny
Overview
Cladistics
Which are clades and which are not?
Constructing a phylogenetic tree based on homology
jaws
lungs
amniotic fur
egg
lamprey
0
0
0
0
shark
1
0
0
0
salamander 1
1
0
0
lizard
1
1
1
0
tiger
1
1
1
1
gorilla
1
1
1
1
human
1
1
1
1
binocular
vision
0
0
0
0
0
1
1
bipedal
0
0
0
0
0
0
1
The branch points represent the common ancestor
 The characteristics are derived characteristics
 Can use physical characteristics for a broad cladogram
 Can use DNA comparisons for a more narrow cladogram (primate
evolution)
o The more similar the sequence, the more recent the common
ancestor
o The more distant the common ancestor, the more time there
was for mutations to take place
III.
Problems reconstructing phylogenies
i. Not all similar traits are homologous, the result of divergent
evolution (synaptomorphy)
 Synaptomorphy = a trait that is similar among
species because the common ancestor of those
species had that trait
b. Some traits evolved by convergent evolution = homoplasy
http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_09
3. Then how can we accurately create phylogenetic trees?
 Must use many traits to construct phylogenetic tree
 If don’t distinguish between homoplasy and homology you will with
wrong conclusions
 homology is more reliable than homoplasy BUT must be able to
distinguish between them
4. Parsimony and constructing phylogenetic trees
 Parsimony: criteria used to construct phylogenetic trees based on
minimizing the number of changes
Constructing trees based on parsimony
vertebrae bony
4
amniotic
hair
two post orbital
skeleton limbs egg
fenestrae
sharks
y
n
n
n
n
ray finned
y
y
n
n
n
n
fish
n
primates
rodents and
rabbits
y
y
y
y
y
y
y
y
y
y
n
crocodiles
y
y
y
y
n
y
dinosaurs
and birds
y
y
y
y
n
y
dinosaurs and birds
Crocsodiles
Rodents and
rabbits
primates
Crocsodiles
amphibians
ray finned fish
sharks
dinosaurs and birds
n
Rodents and
rabbits
n
primates
y
amphibians
y
ray finned fish
y
sharks
amphibians