Phylogeny
AP Biology Topic 7.9
Phylogenetic Trees and cladograms
show the evolutionary relationship
of species over lineages.
Cladogram
These diagrams are
hypotheses of
evolutionary relationships
based on molecular and
morphological data.
Phylogenetic Tree
However,
Phylogenetic Trees
are calibrated using
the fossil record and
molecular clocks to
show the amount of
change.
Let’s look at how to read and understand them…
Present
Time
(or more recent)
Past
Let’s look at how to read and understand them…
These represent
the different
species being
studied.
Common
Ancestor of
A, B, and C
Point of
divergence/
speciation
Common
Ancestor of
A, B, and C
The lines
represent the
series of
ancestors over
time, leading
to the present
day species.
Unique evolutionary
history for species D
Shared evolutionary history for species
B,C, and D, but not A
Shared evolutionary history for
all four species
How to find Common
Ancestors and Relatedness.
B and C are the
most closely related
because they share
the most recent
common ancestor.
Arrow 1 represents the most
recent common ancestor of
all four species, A-D.
Arrow 2 represents the
common ancestor of
B, C, and D
Arrow 3 represents the
common ancestor of
B and C.
B is more closely related to D when compared to A because B and D share a recent common ancestor at #2, which
is more recent in terms of time compared to the recent common ancestor at #1, which is further back in time.
Rotating the species at the different divergence points, doesn’t
change the evolutionary relationships. The distance and
relatedness remain the same.
Rotating the species at the different divergence points, doesn’t
change the evolutionary relationships. The distance and
relatedness remain the same.
All four of the images below all show the
same evolutionary relationships
When “reading” a phylogenetic tree or cladogram, the order
of the species at the top is not the important part, but rather
the locations of the branch points within the tree.
The next question we need to ask,
is “How do we construct a
phylogenetic tree?”
Morphological, biochemical,
molecular, or behavioral
data can be used to
construct a tree.
DNA or amino
acid sequences
Most
accurate &
reliable.
By analyzing the data, we can begin to group
organisms into different species.
Character Table
Trait
Six legs
Blue spots
Antenna
Wings
1
Species
2
3
4
Outgroup: The
lineage that is least
closely related to
the remainder of
the organisms in
the phylogenetic
tree or cladogram.
1
3
Shared derived traits: Traits
that indicate common
Wings
ancestry
2
4
Antenna
Blue dots
Six legs
1
3
2
4
Wings
Antenna
Blue dots
Six legs
Using Molecular Data to Construct a
phylogenetic tree or cladogram
Number of Amino Acid Differences in Protein X
Species A
Species B
Species C
Species D
Species E
Species A
---
Species B
--4
4
---
2
6
---
6
1
5
---
10
11
9
12
---
Species C
Species D
Species E
E
Outgroup
C
A
B
D
E
A
C
B
D