Chapter 20
Phylogenetic Trees
Figure 20.5
Branch point:
where lineages diverge
Taxon A
3
Taxon B
4
Taxon C
Sister
taxa
2
Taxon D
ANCESTRAL
LINEAGE
1
5
Taxon E
Taxon F
Taxon G
This branch point
represents the common
ancestor of taxa A−G.
This branch point forms a
polytomy: an unresolved
pattern of divergence.
Basal
taxon
• Which animal represents the basal taxon?
– Camels
• Which animal is least like the others?
– Camels
• Are pigs and peccaries sister taxa?
– Yes, they share an immediate common ancestor.
• Did baleen whales evolve from toothed whales?
– No! Do not assume that a taxon evolved from the
taxon next to it.
• Which are more closely related, hippos and
toothed whales or hippos and pecorans?
– Hippos and toothed whales
• Which are more closely related, hippos and
toothed whales or hippos and baleen whales?
– You can’t tell from the information given
Leopard (common name)
What level of
classification do
humans share
with leopards?
Species: Panthera pardus
Genus: Panthera
Family: Felidae
Order: Carnivora
Domain
Kingdom
Phylum
Class
Class: Mammalia
Phylum: Chordata
Domain:
Bacteria
Kingdom:
Animalia
Domain:
Eukarya
Domain:
Archaea
Leopard (common name)
What genus is
the leopard in?
Species: Panthera pardus
Panthera
Domain:
Bacteria
Kingdom:
Animalia
Domain:
Eukarya
Domain:
Archaea
Concept 20.2: Phylogenies are inferred from
morphological and molecular data
• The similarities used to infer phylogenies must
result from shared ancestry.
• Bat and bird wings are homologous as forelimbs,
but analogous as functional wings.
Evaluating Molecular Homologies
• Analogous structures or molecular sequences are
also called homoplasies.
• Molecular homologies are determined based on
the degree of similarity in nucleotide sequence
between taxa.
• What happens in a frameshift mutation?
• Systematists use computer programs when
analyzing comparable DNA segments from different
organisms.
Figure 20.8-4
1 CCAT CAGA GTCC
2 CCAT CAGA GTCC
Deletion
1 CCAT CAGA GTCC
2 CCAT CAGA GTCC
G T A Insertion
1 CCAT CAAGTCC
2 CCAT GTA CAG AGTCC
1 CCAT
CA
AGTCC
2 CCAT GTA CAG AGTCC
• Shared bases in nucleotide sequences that are
otherwise very dissimilar are called molecular
homoplasies.
A C GG A T A G T C C A C T A G G C A C T A
T C A C C GA C A G G T C T T T G A C T A G
• About how much DNA would you expect two
species to share based on chance alone?