Download D.5.5-D.10 Cladograms and phylogeny

D.5.5-D.5.10
Phylogeny and classification
http://www.youtube.com/watch?feature=player_embedded&v=F38BmgPcZ_I
Linking Classification and Phylogeny
• Evolutionary relationships in branching
phylogenetic trees -- Called a cladogram
Species
Mephitis
mephitis
(striped skunk)
Lutra lutra
(European
otter)
Genus
Panthera
Mephitis
Lutra
Felidae
Order
Panthera
pardus
(leopard)
Family
LE 25-9
Mustelidae
Carnivora
Canis
familiaris
(domestic dog)
Canis
lupus
(wolf)
Canis
Canidae
Cladogram
• Each branch point represents the divergence of
two species
Evolutionary Relationships/ phylogeny is depicted
in an evolutionary tree/ cladogram
• Evolutionary relationships in branching trees
Evolutionary Relationships/ Phylogeny is depicted
in an Cladogram
• Nodes show that groups share a common
ancestor & evolved from this ancestor
Evolutionary Relationships/ Phylogeny is depicted in an Cladogram
• Each branch point represents the divergence of
two species
Branching
Panthera
Felidae
Order
Genus
Panthera
Mephitis
Lutra lutra
Canis
Canis
pardus
mephitis
(European
familiaris
lupus
(leopard) (striped skunk)
otter)
(domestic dog) (wolf)
Family
Species
Evolutionary Relationships/ Phylogeny is depicted in an Cladogram
Mephitis
Lutra
Mustelidae
Carnivora
Canis
Canidae
This evolutionary
tree shows that
leopards, skunks,
otters, dogs, wolves
all share a
common ancestor.
What other
conclusions can
you make form this
phylogenic tree?
Common Ancestor
Evolutionary Relationships/ Phylogeny is depicted in an Cladogram
• How many common
ancestors does G
and H have?
• three
• How many common
ancestors does G
and E have?
• TWO
• Which pair are
more closely
related G and H
OR G and E?
• G and H share
more ancestors.
• In the below
evolutionary tree
which groups are
more closely related J
and K OR J and H?
• J and K are more
closely related
because they share
two common
ancestors I, A.
• And J and H only
share one common
ancestor, A
• Evolutionary Trees/ Phylogenies also show
relative time.
• The top of the
tree being more
recent.
• The bottom
showing the
distant past
D.5.5 Define Clade and cladistics
• A cladogram depicts patterns of shared
characteristics among taxa
• A clade is a group of species that includes an
ancestral species and all its descendants
• Cladistics studies resemblances among clades
D.5.5 Define Clade and cladistics
• Cladistics: a System of classification which
groups taxa together according to the
characteristics which have most recently evolved.
• Used to decide how close a common ancestor is,
researchers look at how many primitive and
derived traits the organism share.
IB Objective D.5.10
Discuss the relationship between Cladograms & Classification:
•
Classification traditionally based on morphology/ physical characteristics ;
•
While Cladistics is based on molecular differences/base sequences/amino acid
sequences. This is a strength of cladistics because it maintain objectivity;
•
Cladistics is based on probability but improbable events do occur, so relationships
can be wrong; and this is thus a weakness of cladistics;
•
Clades includes ancestral species/descendants from that species;
•
The Members of clade share set of features not found in more distant relatives;
•
Cladogram is a tree-like diagram where nodes/branches represent the splitting of
(two) new groups from a common ancestor;
•
Different cladograms can represent same relationships in a group;
•
Cladogram timescale not necessary;
•
Classification based on cladograms is often same as traditional classification;
•
However, in some groups, cladograms have led to revised classification;
• A valid clade is monophyletic, signifying that it
consists of the ancestor species and all its
descendants
LE 25-10a
Grouping 1
Monophyletic
A monophyletic group = CLADE
D.5.7 Outline methods to construct cladograms
and the conclusions that can be drawn from them
• How cladograms are made
1. Make a list of all the organisms which will be
included in your cladogram
2. List the characteristics each organism
possesses
D.5.7 Outline methods to construct cladograms and the conclusions that can
be drawn from them: How cladograms are made
3. Once the list is made the characteristics common to all
organisms this trait is considered a primitive trait.
4. Then you make a table like the one below:
Multicellular
Vertebral
column
Hair
placenta
total
sponge
✓
x
x
x
1
sailfish
✓
✓
x
x
2
wombat
✓
✓
✓
x
3
elephant
✓
✓
✓
✓
4
STEP 5: USE DATA TABLE TO CONSTRUCT
A VENN DIAGRAM
STEP 6. CONVERT VENN DIAGRAM TO A
CLADOGRAM
D.5.7 Outline the conclusions that can be drawn
from them
– Cladograms are constructed to show
evolutionary relationships between
organisms
– Organisms at the bottom are the earliest ones
– Organisms at the top of the branch are
considered the most recent.
– Biochemical evidence (DNA Similarities) can
be used instead of physical characteristics
65.5
Cenozoic
251
Mesozoic
Millions of
years ago
542
Paleozoic
Neoproterozoic
• Cladograms are
constructed to show
evolutionary
relationships
between organisms
• Organisms at the
bottom are the
earliest ones
• Organisms at the top
of the branch are
considered the most
recent.
Human
Mushroom
Tulip
0
30%
40%
0
40%
Human
Mushroom
Biochemical evidence
Tulip
(DNA Similarities) can
be used instead of Percentage differences between sequences
physical characteristics
0
25%
15%
15%
20%
15%
10%
5%
Tree 1: More likely
Comparison of possible trees
5%
Tree 2: Less likely
LE 25-15ab
Biochemical
I
evidence (DNA
Similarities) can
II
be used instead Species
III
of physical
characteristics
IV
I
Sites in DNA sequence
1 2 3 4 5 6 7
II
III
IV
Bases at
site 1 for
each species
Base-change
event
LE 25-16
Lizard
Bird
Mammal
Four-chambered
heart
Mammal-bird clade
Lizard
Bird
Mammal
Four-chambered
heart
Four-chambered
heart
Lizard-bird clade
D.5.6 Distinguish with example between analogous
characteristics and homologous characteristics
• In constructing a phylogeny/ cladograms, one
needs to distinguish whether a similarity is the
result of homology or analogy
• Homology is similarity due to shared ancestry
• Analogy is similarity due to convergent
evolution
D.5.6 Distinguish with example between analogous
characteristics and homologous characteristics
• Convergent evolution occurs when similar
environmental pressures and natural selection
produce similar (analogous) adaptations in
organisms from different evolutionary lineages
Assignment.
• Make two cladograms:
– First cladogram–PLANTS (topic 5.5) show
the evolutionary/ phylogenic relationships
between bryophytes, filicinophyta,
coniferophyta, angiospermaphyta
– Second Cladogram – Animals (topic 5.5)
show the evolutionary/ phylogenic
relationships between porifera, cnidaria,
platyhelminthes, Annelida, Mollusca,
Arthropoda.
IB Practice Test Question 1
• Define the term clade. (1)
IB Practice Test Question 1 -- Answer
A clade is a group of related organisms sharing a
common ancestor / a group of organisms containing
an ancestor and all of its descendants
IB Practice Test Question 2
• Suggest two reasons for using cladograms for the
classification of organisms.(2)
IB Practice Test Question 2 -- Answer
• Methods used to prepare cladograms use a
different approach from traditional
classification/taxonomy;
• Cladograms show ancestral relationships;
• Cladograms reflect how recently two groups
shared a common ancestry;
• cladograms are (objective/accurate because they
are usually) based on molecular differences
(e.g. differences in DNA/ RNA Proteins);
• Cladograms should be considered as a good
complement to traditional classification;
IB Practice Test Question 3
• Using examples, distinguish between analogous
characteristics and homologous characteristics.(4)
IB Practice Test Question 3 -- Answer
Analogous Structures: [2 max]
• similar structures but different (evolutionary)
origins / different basic structure but same
function;
• e.g. vertebrate and invertebrate eyes / insect and
human legs; Accept any other valid example.
Homologous Structure: [2 max]
• structures are of similar origin / same basic
structure but different functions;
• e.g. pentadactyl limbs in vertebrates; Accept any
other valid example.
IB Practice Question 4
• The cladogram below shows the classification of
species A to D. Deduce how similar species A is to
species B, C and D. (2)
•
IB Practice Question 4 -- Answer
• A is most similar to B;
A is equally similar to C and D;
A is least similar to both C and D;
IB Practice Test Question 5
Outline the evidence provided by DNA for the
common ancestry of living organisms. (2)
Practice Test Question 5-- Answer
• all living organisms use DNA as genetic/hereditary
material;
• genetic code is universal (e.g. nitrogenous bases
code for proteins);
• The idea that mutations accumulate gradually in
DNA; and thus the more differences there are in
DNA between species the longer the time it has
been since those species shared a common
ancestor;
IB Objective D.5.10
Discuss the relationship between Cladograms & Classification:
•
Classification traditionally based on morphology/ physical characteristics ;
•
While Cladistics is based on molecular differences/base sequences/amino acid
sequences. This is a strength of cladistics because it maintain objectivity;
•
Cladistics is based on probability but improbable events do occur, so relationships
can be wrong; and this is thus a weakness of cladistics;
•
Clades includes ancestral species/descendants from that species;
•
The Members of clade share set of features not found in more distant relatives;
•
Cladogram is a tree-like diagram where nodes/branches represent the splitting of
(two) new groups from a common ancestor;
•
Different cladograms can represent same relationships in a group;
•
Cladogram timescale not necessary;
•
Classification based on cladograms is often same as traditional classification;
•
However, in some groups, cladograms have led to revised classification;