Download Chapter 26

Chapter 26
Phylogeny and the Tree of Life
Objective
SWBAT explain and demonstrate that
organisms share many conserved core
processes and features that evolved and
are widely distributed among organisms
today.
Agenda
1.
2.
3.
Chapter 25 Quiz
Chapter 26 notes: sections 26.1, 26.2, and
26.3
Guided practice with phylogeny
Homework:
a) Phylogeny Worksheet. Due Monday,
September 22
b) Read all of Chapter 26 this weekend for
Monday.
4.
Phylogeny and the Tree of Life
Chapter 26
http://www.youtube.com/watch?v=H6IrUUDboZo
The Origin of Species
As buds give rise by growth to
fresh buds, and these, if
vigorous, branch out and
overtop on all sides many a
feebler branch, so by
generation I believe it has
been with the great Tree of Life,
which fills with its dead and
broken branches the crust of
the earth, and covers the
surface with its ever-branching
and beautiful ramifications. ~
Charles Darwin
Darwin’s Tree of Life
Evolution as a branching, tree-like process
A phylogenetic tree of the
bacterial domain.
A phylogenetic tree
represents a hypothesis of
the order in which
evolutionary events are
assumed to have occurred.
Phylogenetics

Phylogenetics is the study of evolutionary relatedness
among various groups of organisms, which is discovered
through molecular sequencing and morphological data.
Tucuxi
What do phylogenetic trees
represent?
Madison DR (2012) Phylogeny of Bembidion and related ground beetles. Molecular Phylogenetic and Evolution 64:553-576
Going back in time…
Present
Past
2 leaves…
on connecting branches
How can we hypothesize that this speciation
event occurred ~ 1.5 million years ago?
The key is in the DNA
Species vary in their gene pools (the
alleles for all traits)
 The gene pool of a population changes
over time
◦ natural selection
◦ genetic drift
◦ genetic recombination
◦ mutation

Mutation

Change in nucleotide sequence of an
organism’s DNA
Molecular clock



The mutation rates of particular genes are relatively
constant, thus the rate of mutations can be used as a
molecular clock
If mutation rates are constant, then we can use such
genes to extrapolate when speciation events took
place
Example: The gene that codes for hemoglobin
experiences 0.56 changes per base pair per billion
years
The cytochrome c gene
reflects a pattern of
differences in DNA
sequences due to
mutations.
The changes accumulate
at a constant rate, and
can be used as a
molecular clock to help
date evolutionary
divergences.
Figure 26.4
Order
Family Genus
Species
Panthera
Felidae
Panthera
pardus
(leopard)
Taxidea
Lutra
Mustelidae
Carnivora
Taxidea
taxus
(American
badger)
Lutra lutra
(European
otter)
Canis
Canidae
Canis
latrans
(coyote)
Canis
lupus
(gray wolf)
Figure 26.10
(a) Monophyletic group (clade)
(b) Paraphyletic group
(c) Polyphyletic group
A
A
B
B
C
C
C
D
D
D
E
E
F
F
F
G
G
G
A
B
Group 
Group 
E
Group 
2 leaves…
on connecting branches
How can we hypothesize that this speciation
event occurred ~ 1.5 million years ago?
Answer: Use the amount of variability
between DNA sequences to estimate
the time of speciation events
The evolution of HIV
1884 – 1924
HIV jumped from chimps to humans
1966
Africa  Haiti  U.S. (Robert R., first
HIV/AIDS death in U.S., 1969)
2010
Evidence that a newer strain of HIV
jumped to humans from gorillas
http://evolution.berkeley.edu/evolibrary/news/081101_hivorigins
We can also use morphological
differences to deconstruct evolutionary
relationships
Derived
Ancestral
We can also use morphological
differences to deconstruct evolutionary
relationships
Derived
Ancestral
Hair is a shared derived trait
(synapomorphy) of mammals
Parsimony: evolution takes the easier
path
Parsimony: evolution takes the easier
path
Guided Practice on Parsimony: which
one is the most parsimonious tree?
Parsimony: evolution takes the easier
path
Guided Practice: What is the difference
between these trees?
A
C
B
A
B
C
B
C
A
Guided Practice: What is the difference
between these trees?
A
C
B
A
B
C
B
C
A
They are all the same. B and C are sister species. In
addition, A, B, and C share a common ancestor in
all trees.
Guided Practice: What is the difference
between these trees?
What is the difference between these trees?
They are all the same. Humans, chimps, and common ancestor 1 are
monophyletic. Gorillas are an outgroup to humans and chimps. Orangutans
are also an outgroup to common ancestor 2 and its descendants.
Using phylogenetics to solve a crime
Summary
Phylogeny is the evolutionary history of a
species or group of related species
 The discipline of systematics classifies
organisms and determines their evolutionary
relationships
 Systematists use fossil, molecular, and genetic
data to infer evolutionary relationships

Binomial Nomenclature
In the 18th century, Carolus Linnaeus
published a system of taxonomy based on
resemblances
 Two key features of his system remain useful
today: two-part names for species and
hierarchical classification

Figure 26.3
Species:
Panthera pardus
Genus:
Panthera
Family:
Felidae
Order:
Carnivora
Class:
Mammalia
Phylum:
Chordata
Domain:
Bacteria
Kingdom:
Animalia
Domain:
Eukarya
Domain:
Archaea