- A cladogram shows patterns of shared characteristics among species and groups them into clades based on shared ancestry. There are three types of clades: monophyletic, paraphyletic, and polyphyletic. - When constructing phylogenetic trees, systematists apply principles of maximum parsimony and maximum likelihood to find the tree that requires the fewest evolutionary changes or is most likely given patterns of DNA change over time. - Strongest phylogenetic hypotheses are supported by morphological, molecular, and fossil evidence from multiple sources.

2. -Cladogram: shows patterns of shared
characteristics
-Clade: a group of species including
ancestral and descendants in the tree

4.  I. Monophyletic: regular clade
 II. Paraphyletic: ancestor is present, but
not all descendants
 III. Polyphyletic: descendants are
present, but no ancestor

5. D E G H J K
C F I
B
A

6. D E G H J K
C F I
B
A

7. D E G H J K
C F I
B
A

8.  ―Character‖ refers to any feature that a
particular taxon process
 Shared primative character – A
character that is shared beyond the
taxon we are trying to define
 Shared derived character – An
evolutionary novelty unique to a
particular clade

9.  Outgroup comparison is used to
differentiate between shared derived
characters and shared primitive
characters
 Ingroup – The various species we are
studying
 Outgroup – A species or group of
species that is closely related to the
ingroup.

10.  Phylograms – present sequences of
events relative to each other.
 Ultrametric Trees – Present sequences
based on the actual times they
occurred.

11.  Length of branch corresponds to the
amount of changes that occurred.
 A long branch means more changes in
DNA.

13.  The lengths of the branches are the
same lengths for each lineages.
 The tree draws information from the fossil
record.

14. Proterozoic Paleozoic Mesozoic Cenozoic
Millions of 542 251 65.5
years ago

15.  Systematists:
› Can never be sure of finding the single best tree in a large
data set.
› Narrow the possibilities by applying the principles of
maximum parsimony and maximum likelihood.
 According to the principle of maximum parsimony, we
should first investigate the simplest explanation that is
consistent with the facts.
 The principle of maximum likelihood states that, given certain
rules about how DNA changes over time, a tree can be
found that reflects the most likely sequence of evolutionary
events.
 Among phylogenetic hypotheses

16. Human Mushroom Tulip
Human 30%
0 40%
Mushroom
0 40%
0
Tulip
(a) Percentage differences between sequences
Figure 25.14 (a)

17. 25%
15%
15% 15% 20%
10%
5% 5%
Tree 1: More likely Tree 2: Less likely
(b) Comparison of possible trees
Figure 25.14 (b)

18.  Phylogenetic trees represent a possible
way of how the species in it are related.
 Phylogenetic hypotheses can change
with new evidence.
 Usually the most parsimonious tree is
most likely
 Analogy-Homology issue
 The more matching base pairs the less
probability they evolved independently

19.  Parsimony more reliable if with longer
segments.
 Accidentally mistaking an analogy for a
homology is less likely to affect the tree if
the clades are defined by several
defined characters.
 Strongest hypotheses are supported by
lots of morphological and molecular
evidence and fossil evidence.
 Pg.502-503

20. APPLICATION In considering possible phylogenies for a group of species, systematists compare molecular data for the species. The
most efficient way to study the various phylogenetic hypotheses is to begin by first considering the most parsimonious—that is, which
hypothesis requires the fewest total evolutionary events (molecular changes) to have occurred.
TECHNIQUE Follow the numbered steps as we apply the principle of parsimony to a hypothetical phylogenetic
problem involving four closely related bird species.
1 First, draw the possible phylogenies for the species
(only 3 of the 15 possible trees relating these four
species are shown here).
Species Species Species Species
I II III IV
I II III IV I III II IV I IV II III
Three possible phylogenetic hypothese
Sites in DNA sequence
1 2 3 4 5 6 7
2 Tabulate the molecular data for the species (in this simplified I A G G G G G T
example, the data represent a DNA sequence consisting of
just seven nucleotide bases). II G G G A G G G
Species
III G A G G A A T
IV G G A G A A G
I II III IV
A G G G
Bases at
site 1 for
each species
3 Now focus on site 1 in the DNA sequence. A single base- G G
change event, marked by the crossbar in the branch leading Base-change
to species I, is sufficient to account for the site 1 data. event
G

21. THE END.