Transcript Phylogeny and Classification

Classification
Hierarchical classification
Species
Panthera
Genus
Felidae
Family
Carnivora
Order
Class
Phylum
Kingdom
Domain
Panthera
pardus
Mammalia
Chordata
Animalia
Eukarya
Species
Panthera
Order
Family
Mephitis
Panthera
Canis
Canis
Lutra lutra
mephitis
pardus
familiaris
lupus
(European
(leopard) (striped skunk)
otter) (domestic dog) (wolf)
Genus
The connection between classification
and phylogeny
Felidae
Mephitis
Lutra
Mustelidae
Carnivora
Canis
Canidae
Monophyletic, paraphyletic, and
polyphyletic groupings
Grouping 2
Grouping 1
D
E
G
C
H
J
F
K
I
B
D
E
G
C
H
J
F
K
I
B
A
(a) Monophyletic. In this tree, grouping 1,
consisting of the seven species B– H, is a
monophyletic group, or clade. A monophyletic group is made up of an
ancestral species (species B in this case)
and all of its descendant species. Only
monophyletic groups qualify as
legitimate taxa derived from cladistics.
Grouping 3
D
E
G
C
H
J
F
K
I
B
A
A
(b) Paraphyletic. Grouping 2 does not
meet the cladistic criterion: It is
paraphyletic, which means that it
consists of an ancestor (A in this case)
and some, but not all, of that ancestor’s
descendants. (Grouping 2 includes the
descendants I, J, and K, but excludes
B–H, which also descended from A.)
(c) Polyphyletic. Grouping 3 also fails the
cladistic test. It is polyphyletic, which
means that it lacks the common ancestor
of (A) the species in the group. Furthermore, a valid taxon that includes the
extant species G, H, J, and K would
necessarily also contain D and E, which
are also descended from A.
Not all Similarities Represent
Common Ancestry
• Homologous structures indicate shared
common ancestry
• Homologous structures are therefore
evidence of divergent evolution
• Analogous structures are similar in function
but not in evolutionary history
• Analogous structures are evidence of
convergent evolution
• It is not always easy to sort homologous from
analogous structures
How would you compare the fins in
these 2 organisms?
In what way are these organisms displaying
examples of convergent evolution?
• How do we differentiate between homologous
and analogous structures?
• Compare embryonic development of the
structures in question
• Look for structures that are complex.
• The more complex the structures are the more
likely that they are homologous.
• Compare macromolecules along with
anatomical features.
Phenetics
• Phenetics =
– compares many anatomical characteristics
to (overall phenotype) to construct
phylogeny
– Does not sort homologous from analogous
structures.
• phylogenetic trees
Cladistics
• Cladistics =
– sorts homologous from analogous
structures
– sorts primitive and shared derived
characteristics
Shared Derives Characteristics
• Need to differentiate between shared
primitive characters and shared derived
characters
Analogies
All similar
characters
Primitive
(ancestral)
Homologies
Derived
(unique to
a clade)
Outgroups
• Distinguishes between shared primitive
and shared derived characteristics
• Closely related to ingroup
Building a Cladogram
What is the shared primitive characteristic?
Notochord
Does not mean that turtles evolved more recently than salamander
Parsimony and the analogyversus-homology pitfall
Bird
Lizard
Parsimony does not
always work, nature does
not always take the
simplest course
Mammal
Four-chambered
heart
(a) Mammal-bird clade
Lizard
Bird
Mammal
Four-chambered
heart
Four-chambered
heart
(b) Lizard-bird clade
Modern Systematics
Aligning segments of DNA
1 Ancestral homologous
DNA segments are
identical as species 1
and species 2 begin to
diverge from their
common ancestor.
1 C C A T C A G A G T C C
2 C C A T C A G A G T C C
Deletion
2 Deletion and insertion
mutations shift what
had been matching
sequences in the two
species.
1 C C A T C A G A G T C C
2 C C A T C A G A G T C C
G T A
3 Homologous regions
(yellow) do not all align
because of these mutations.
4 Homologous regions
realign after a computer
program adds gaps in
sequence 1.
1
C C A T
2
C C A T
1
C C A T
2
C C A T
Insertion
C A
G T A
G T A
A G T C C
C A G
A G T C C
C A
A G T C C
C A G
A G T C C
Bird Phylogenetic Tree
• And sometimes the simplest explanation is
not the best…
Hominidae
Pongidae
Classical
Taxonomy
Hominidae
Cladistic
Taxonomy
Pongidae
Trees with different likelihoods
Tree 2
assumes
different rates
of DNA
changes
Molecular Clocks
• Proteins and mitochondrial genomes have
constant rate of change over time
• Use these rates to determine relative
evolutionary relatedness.
Review Questions
•
1. The temperature at which hybrid DNA melts is
indicative of the degree of homology between the
DNA sequences. The more extensive the pairing,
the higher the temperature required to separate
the strands. You are trying to determine the
phylogenetic relationships among species A, B,
and C. You mix single-stranded DNA from all
three species (in test groups of two) and measure
the temperatures at which the hybrid DNA melts
(separates). You find that hybrid BC has the
highest melting temperature, AC the next highest,
and AB the lowest.
• (cont.) From these data you conclude that *
A. species A and B are most closely related, whereas B
and C are least closely related.
B. B and C must be the same species, and A is more
closely related to C than to B.
C. species B and C must have diverged most recently,
and A is more closely related to C than to B.
D. A hybridizes most easily with B, and they must have
a more recent common ancestor than do A and C.
E. these tests are inconclusive and you had better go
back and check the fossil record.
•
2. According to this dichotomous phylogenetic tree
created using cladistic analysis, C and D are most
closely related because they
A. do not share a common
ancestor with O, A, or B.
B. are monophyletic.
• evolved from a common
ancestor a long time
ago.
• have the most shared
derived characters in
common.
• have the greatest
number of anatomical
similarities as shown by
statistical analysis.
• 3. A biologist discovers two new species of
organisms, one in Africa and one in South America.
The organisms resemble one another closely. Which
type of evidence would probably be least useful in
determining whether these organisms are closely
related or are the products of convergent evolution?
A.
B.
C.
D.
E.
the history and timing of continental drift
a comparison of DNA from the two species
the fossil record of the two species
analysis of the behavior of the two species
comparative embryology
• Use Figure 25.1 to answer the following
questions.
4. A common ancestor for species C and E
could be at position number
•
•
•
•
•
1.
2.
3.
4.
5.
• E. The two extant species that are most
closely related to each other are
1.
2.
3.
4.
5.
A and B.
B and D.
C and B.
D and E.
E and A.
•
5. If this evolutionary tree is an accurate depiction of
relatedness, then which of the following should be correct?
A. The entire tree depicts
anagenesis.
B. If all species depicted
here make up a taxon,
this taxon is
monophyletic.
C. The last common ancestor
of species B and C occurred
more recently than the last
common ancestor of species
D and E.
D. Species A is the ancestor of
both species B and C.
E. The species present at position number
three is ancestral to three extant species.
1.
2.
•
•
•
B only
A and C
C and D
B, C, and D
B, C, and E
• A researcher compared the nucleotide
sequences of a homologous gene from five
different species of mammals. The sequence
homology between each species' version of the
gene and the human gene are presented as a
percentage of similarity.
Species
Percentage
Chimpanzee
99.7
Orangutan
98.6
Baboon
97.2
Rhesus Monkey
96.9
Rabbit
93.7
•
6. What conclusion can be validly drawn from
these data?
A. Humans and other primates evolved from rabbits.
B. All organisms have similar DNA.
C. Among the organisms listed, humans shared a
common ancestor most recently with
chimpanzees.
D. Humans evolved from chimpanzees.
E. Both A and D are correct.
• 7. Which statement represents the best
explanation for the observation that the nuclear
DNA of wolves and domestic dogs has a very high
degree of homology?
A. Dogs and wolves have very similar
morphologies.
B. Dogs and wolves belong to the same genus.
C. Dogs and wolves are both members of the family
Canidae.
D. Dogs and wolves shared a common ancestor
relatively recently.
E. Convergent evolution has occurred.