Warm-Up
1. Contrast adaptive radiation vs. convergent evolution?
Give an example of each.
2. What is a 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
Ch 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
• Dumb King Philip Came
Over From Germany Sailing
• Your own???
Phylogenetic Tree
• Branching diagram that shows evolutionary
history of a group of organisms
Activity: Constructing a Cookie
Phylogenetic Tree
Activity: Constructing a Cookie
Phylogenetic Tree
Living (extant) species
Common
ancestor
(fossil)
Extant species
Common
ancestor
Example of a Cookie Tree
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
Need help? See next slide
Need more help understanding
phylogenetic trees/cladograms?
• Take a visit to the ‘Tree Room’!
http://evolution.berkeley.edu/evolibrary/article
/0_0_0/evotrees_intro
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
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:
Various tree layouts
Circular (rooted) tree
Unrooted tree
Rooted tree
• 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
▫ Ex. Origin of HIV infection in humans= 1930’s
▫ What is a major problem with a molecular clock?
Tree of Life
• 3 Domains: Bacteria, Archaea, Eukarya
• Tool for Classification: Dichotomous Key
http://www.biologycorner.com/worksheets/pamishan.html
Definition:
• Dichotomous Key: uses
contrasting characteristics to
determine the identity of an
organism by dividing the
organisms in the key into
smaller and smaller groups;
each time a choice is made, a
number of organisms are
eliminated. If sufficient
characteristics are contrasted,
the number of possibilities for
the identity of the unknown
organism is eventually reduced
to one.
Example
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