Ch. 26- Phylogeny and the Tree of Life

Ch. 26- Phylogeny and the Tree of Life- Guided Notes
What you must 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.
Ch 26 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. Use the four cladograms below to answer the following questions:
a. Which cladograms have identical topologies (show the same pattern of relationships)?
b. On tree 1, circle two different monophyletic groups.
c. On tree 4, which organisms are more closely related B and C or C and D. How can you tell?
1. Systematics
• Systematics: classifying organisms and determining
their evolutionary relationships
2. Tools used to determine evolutionary relationships:
• Fossils
• Morphology (homologous structures)
o In constructing a phylogeny, systematists need
to distinguish whether a similarity is the result
of homology or analogy
 Homology is similarity due to shared
 Analogy is similarity due to
convergent evolution
• Molecular evidence (DNA, amino acids)
Question: Who is more closely related? Answer: Animals
and fungi are more closely related than either is to plants.
3. Taxonomy
Taxonomy: science of classifying
and naming organisms
Binomial nomenclature
(Genus species)
Naming system developed by
Carolus Linnaeus.
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???
4. Phylogenetic Trees
• Phylogenetic Tree: Branching diagram that shows evolutionary history of a group of organisms
• Each branch point represents the divergence of two species
• “Deeper” branch points represent progressively greater amounts of divergence
Simple Example trees
5. Phylogenetic Tree Varieties
Branch length does not indicate evolutionary
change or time
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
Rooted tree
6. Constructing a phylogenetic tree
 A 0 indicates a character is absent; a 1 indicates that a character is present.
Unrooted tree
Branch lengths can represent genetic change
7. Practice: Build your own tree
Branch lengths can indicate time
Practice: 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
8. Cladogram
• Cladogram: diagram that
depicts patterns of shared
characteristics among taxa
• Clade = group of
species that includes an
ancestral species + all
• Shared derived
characteristics are used
to construct cladograms
• A shared primitive
character- is a character
that is shared beyond
the taxon being defined
• A shared derived
character- is an
evolutionary novelty
unique to a particular
9. Groupings
• Monophyletic groupconsists of the ancestor
species and all its
• Paraphyletic group- consists
of an ancestral species and
some, but not all, of the
• Polyphyletic group- consists
of various species that lack
a common ancestor
• Outgroup- 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
between shared
derived and shared
Amniotic egg
Four walking legs
Hinged jaws
Lancelet (outgroup)
Vertebral column
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
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.)?
10. Principle of Maximum Parsimony
• Principle of maximum parsimony: use simplest
explanation (fewest DNA changes) for tree – “keep it
• 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
11. Tree of Life
• 3 Domains: Bacteria, Archaea, Eukarya