Warm-Up
1. Contrast adaptive radiation vs. convergent evolution?
Give an example of each.
2. What is the correct sequence from the most
comprehensive to least comprehensive taxon?
3. In a population of 500 rabbits, 320 are homozygous
dominant for brown coat color (BB), 160 are
heterozygous (Bb), and 20 are homozygous white (bb).
a. What are the frequencies of the alleles (B and b)?
b. What are the frequencies of the different genotypes (BB,
Bb, and bb)?
Chapter 26
Phylogeny and the Tree of Life
What you need to know:
• The taxonomic categories and how they indicate
relatedness.
• How systematics is used to develop phylogenetic
trees.
• The three domains of life including their
similarities and their differences.
Systematics: classifying organisms and
determining their evolutionary
relationships
Taxonomy
(classification)
Systematics
Phylogenetics
(evolutionary history)
Tools used to determine evolutionary relationships:
1. Fossils
2. Morphology (homologous structures)
3. Molecular evidence (DNA, amino acids)
Who is more closely related?
Animals and fungi are more
closely related than either is
to plants.
Taxonomy: science of classifying and
naming organisms
• Binomial nomenclature (Genus species)
Naming system developed by
Carolus Linnaeus.
REMEMBER!!
• Dear King Philip Came Over
For Good Spaghetti
• Dear King Philip Crossed
Over Five Great Seas
• Dear King Philip Came Over
From Germany Stoned
• Your own???
Phylogenetic Tree
• Branching diagram that shows evolutionary
history of a group of organisms
Simple trees
European wildcat
Domestic cat
South China Tiger
IMAGES FROM: Wikimedia Commons
Ancestor of
domestic cat and
wildcat
Domestic cat
European wildcat
Ancestor of all
three cats
Tiger
Human
Gorilla
Chimpanzee
IMAGES FROM: Wellcome Images / Wikimedia Commons
Extant species
Hypothetical ancestors
Human
Chimpanzee
Root
(common
ancestor)
Branch
Gorilla
Outgroup
Cladogram
Branch length does not
indicate evolutionary
change or time
Phylogram
Branch length shows
evolutionary change or
time (or both)
Unrooted tree
Only relationships
are shown
Rooted tree
Relationships and the
order of events are
shown
Three possible layouts
Circular (rooted) tree
Unrooted tree
Rooted tree
Constructing a phylogenetic tree
A 0 indicates a character is absent; a 1
indicates that a character is present.
Branch lengths can represent genetic change
Branch lengths can indicate time
Build your own tree
Living (extant) species
Common
ancestor
(fossil)
Extant species
Common
ancestor
Possible answers
Tree 1
Tree 2
Tree 3
Problems
Convergent evolution
Retina
Nerve
fibres
Nerve
fibres
Retina
Optic
nerve
Optic
nerve
Blind
spot
Vertebrate eye
Octopus eye
IMAGE FROM: Caerbannog. Wikimedia Commons
Rhesus monkey
Bacterium
Tiger
Squid
Herring
Snail
Dog
Coelacanth
Lemur
Fox
Turbot
Chimpanzee
Cat
Gibbon
Octopus
Baboon
Redwood tree
Pine tree
Oak tree
Human
With 20 species
8, 200, 794, 532, 637, 891, 559, 375
different trees are possible
Only one is right
Bacterium
Coelacanth
Cat
Tiger
Dog
Fox
Baboon
Rhesus monkey
Chimpanzee
Human
Gibbon
Lemur
Herring
Turbot
Snail
Octopus
Squid
Redwood tree
Pine tree
Oak tree
Draw a phylogenetic tree based on the data below. Draw
hatch marks on the tree to indicate the origin(s) of each of
the 6 characters.
Answer:
Cladogram: diagram that depicts patterns
of shared characteristics among taxa
• Clade = group of species that includes an ancestral
species + all descendents
• Shared derived characteristics are used to construct
cladograms
Turtle
Leopard
Hair
Salamander
Amniotic egg
Tuna
Four walking legs
Lamprey
Lancelet (outgroup)
Cladogram
Hinged jaws
Vertebral column
Monophyletic, paraphyletic, and polyphyletic
groups
Monophyletic
• A valid clade is monophyletic, signifying that it
consists of the ancestor species and all its
descendants
Paraphyletic
• A paraphyletic grouping consists of an ancestral
species and some, but not all, of the descendants
Polyphyletic
• A polyphyletic grouping consists of various
species that lack a common ancestor
Outgroups
• An outgroup is a species or group of species that is
closely related to the ingroup, the various species
being studied
• Systematists compare each ingroup species with the
outgroup to differentiate between shared derived
and shared primitive characteristics
• Outgroup comparison assumes that homologies
shared by the outgroup and ingroup must be
primitive characters that predate the divergence of
both groups from a common ancestor
• It enables us to focus on characters derived at
various branch points in the evolution of a clade
Practice
• Use the four cladograms below to answer the following questions: (5)
• a. Which cladograms have identical topologies (show the same pattern of relationships)?
• b. On tree 1, circle two different monophyletic groups.
• c. On tree 2, can you circle those same monophyletic groups. If so, do it!
• d. On tree 3 circle a paraphyletic group.
• E. On tree 4, which organisms are more closely related B and C or C and D. How can you tell?
More Practice
• Answer the questions associated with the following tree:
• a. Circle the monophyletic group that includes Mimes & Carnies.
• b. Which group(s) are most closely related to Carnies?
• c. Are Clowns, Jugglers & Comedians a monophyletic group? If not, who else would need to be
included?
• d. Who is more closely related to Jugglers: Mimes or Clowns, or are they equally related?
• e. What type of trait is “uses face paint” (e.g. shared ancestral, derived, etc.)?
• Principle of maximum parsimony: use simplest
explanation (fewest DNA changes) for tree –
“keep it simple”
• Molecular clocks: some regions of DNA appear
to evolve at constant rates
▫ Estimate date of past evolutionary events
▫ Eg. Origin of HIV infection in humans= 1930’s
Tree of Life
• 3 Domains: Bacteria, Archaea, Eukarya
SYSTEMATICS
phylogeny
Biological diversity
taxonomy
cladistics
classification
Identification
of species
binomial
Genus, species
D
K
P
C
O
F
G
S
Homologous
similarities
fossils
molecular
morphology