1. Phylogeny and Systematics LECTURE #33
(Making “Trees of Life”) Honors Biology Ms. Day

2. Evolutionary Classification
Phylogeny = the study of evolutionary relationships
Biologists now group organisms into categories that represent evolutionary descent (and not just physical similarities)
How would you classify a hyena?
Would you group it with cats or dogs?
Photo credit flickr: ibeatty

3. Currently, scientists use
Morphological, biochemical (ex: DNA), and molecular comparisons to infer evolutionary relationships
Obtained through fossil studies, DNA technology and current organisms

4. Why do you arrange shared histories?
Uses evidence from
fossil record
Anatomy of existing organisms
DNA/amino acid sequences (proteins)
Use branching “trees” to reflect phylogeny and place groups of closer related organisms into clades
Clade= group of closely related species

5. A cladogram
a picture (“tree”) of shared characteristics among groups of different organisms
A clade within a cladogram
a group of species that includes an ancestral species & all its descendants
Cladistics
the study of resemblances among clades

6. Taxonomy An ordered division of organisms grouped into categories based on a set of characteristics used to assess similarities and differences

7. Linking Classification and Phylogeny
Panthera pardus (leopard)
Mephitis mephitis (striped skunk)
Lutra lutra (European otter)
Canis familiaris (domestic dog)
Canis lupus (wolf)
Panthera
Mephitis
Lutra
Canis
Felidae
Mustelidae
Canidae
Carnivora
Order
Family
Genus
Species

8. Each branch point Represents the divergence of two species Leopard
Domestic cat
Common ancestor

9. “Deeper” branch points
Represent progressively greater amounts of divergence
Leopard
Domestic cat
Common ancestor
Wolf

10. Cladistics Cladogram is a tree with two way branch points
Each branch point represents divergence from common ancestor
Each branch is called a clade
Can be nested within larger clades

12. Making “Trees” similarities based on shared ancestries
bone structure
DNA sequences
beware of analogous structures
SAME function DIFFERENT development (opposite of homologous structures)
This is a result of convergent evolution
bonu/cladograms/Open-This-File.swf

13. Not all Similarities Represent Common Ancestry
Homologous structures indicate shared common ancestry
Homologous structures are therefore evidence of divergent evolution
Analogous structures are similar in function but not in evolutionary history
Analogous structures are evidence of convergent evolution
It is not always easy to sort homologous from analogous structures

14. How do we differentiate between homologous and analogous structures?
Compare embryonic development of the structures in question
Compare macromolecules along with anatomical features called comparative molecular biochemistry.

15. Making “Trees” (Con’t)
A shared primitive character
A structure that is shared by all groups we are trying to define
A shared derived character
A new evolved trait unique to a particular clade(s)

16. What is the shared primitive characteristic? Notochord