Ch. 19: Phylogeny Notes
Taxonomy

Developed by Linnaeus

Taxon = the general name for a group containing an organism or group of
organisms that exhibit a set of shared traits
Phylogeny = an evolutionary family tree that represents the history of taxa

Two Goals:
1) Assigning a each species with a binomial nomenclature (2-name name) called
the specific epithet
First name = Genus
(ex. Felis)
Second name = species
(ex. leo)
Final name: Felis leo
2) Creating a filing system to group species
o Overall hierarchy
Kingdom  Phylum  Class  Order  Family  Genus  Species

The longer these match, the more closely two species are related
o New evidence has led to the development of a higher taxonomic category:
the Domain

Due to fact that Archaea and Bacteria are less alike than previously
thought, leading to the need to separate their kingdom
The 3 Domain System
Domain Bacteria
Domain Archaea
No
No
Membrane Lipids
Phospholipids
Various Branched Lipids
Cell Walls with mostly…
Peptidoglycan
No peptidoglycan
Various
Extremes:
Nuclear Envelopes or
membrane-bound organelles?
Environments
HOT, SALTY or ACIDIC
Domain Eukarya

Includes all remaining organisms, which are eukaryotes

May be multicellular or unicellular, heterotrophic or autotrophic, sexual or
asexual
o Multi- or uni-cellular, hetero- or autotrophic, but SIMPLE…Protists
o Multicellular, AUTOtrophic…Plants
o Multicellular, heterotrophic, ABSORB their food…Fungi
o Multicellular, heterotrophic, INGEST their food…Animals
Phylogenetic Trees


In general, larger groups should break into other groups, creating finer and finer
branches on the tree
The Key to Classifying Organisms
o Monophyletic = a single common ancestor gave rise to all species in that
taxon and to no species placed in any other taxon

This is the best case scenario and the goal of phylogeny
o Lineage = each branch
o Ancestral Traits = those found in the common ancestor and its descendants
o Derived Traits = Those not found in the common ancestor (arose later)

Most important for clarifying evolutionary relationships
Cladistics = method of using shared, derived traits to develop a hypothesis for an
evolutionary history
 Shown in a cladogram
o Clade = a common ancestor and all it descendant lineages
 Applies concept of parsimony = the simplest explanation is usually correct
 Uses outgroup comparisons = a taxon in a lineage that does NOT have a
characteristic that all the others do
o Relies on information from:
 Fossil traits
 Homologous structures
 Must be careful of analogous traits from convergent
evolution
 Behavioral Traits
 Molecular/Biochemical Evidence (DNA, RNA, or Protein
comparisons)
 Mitochondrial DNA (mtDNA) is the best to use for closely
related species, since it mutates 10x faster than nuclear
DNA
 Can be used to create a Molecular Clock = when mutations
accumulate at a fairly constant rate, they can be used to help
determine a timeline of evolutionary history
 Ex. If two songbird subspecies have mtDNA with 5.1%
differences, and we know that the average rate at which
their mtDNA nucleotide changes, then we can calculate
how long ago the two subspecies diverged