Phylogeny and classification D.5.5-D.5.10.
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Phylogeny and classificationhttp://www.youtube.com/watch?feature=player_embedded&v=F38BmgPcZ_I
D.5.5-D.5.10D.5.5-D.5.10
Linking Classification and Phylogeny
• Evolutionary relationships in branching phylogenetic trees -- Called a cladogram
LE 25-9
Carnivora
Pantherapardus
(leopard)
Mephitismephitis
(striped skunk)
Lutra lutra(European
otter)
Canisfamiliaris
(domestic dog)
Canislupus(wolf)S
pec
ies
Gen
us
Fam
ilyO
rder
Felidae Mustelidae Canidae
Panthera Mephitis Lutra Canis
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
Carnivora
Pantherapardus
(leopard)
Mephitismephitis
(striped skunk)
Lutra lutra(European
otter)
Canisfamiliaris
(domestic dog)
Canislupus(wolf)
Sp
ecie
sG
enu
sF
amily
Ord
er
Felidae Mustelidae Canidae
Panthera Mephitis Lutra Canis
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.
Evolutionary Relationships/ Phylogeny is depicted in an CladogramEvolutionary Relationships/ Phylogeny is depicted in an Cladogram
• 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.5.10Discuss 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
Droso
phila
Lanc
elet
Fish
Amph
ibia
nBird
Human
Rat Mou
se
Ce
no
zoic
Me
so
zoic
Pa
leo
zoic
65
.52
51
54
2
Ne
op
rote
rozo
ic
Mil
lio
ns
of
ye
ars
ag
o
• 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
0
Mushroom
30%
0
Tulip
40%
40%
Human
Mushroom
0Tulip
Percentage differences between sequences
Comparison of possible trees
15% 15% 20%
5% 5%
10%
15%
25%
Tree 1: More likely Tree 2: Less likely
Biochemical evidence (DNA Similarities) can be used instead of physical characteristics
LE 25-15ab
Sites in DNA sequence
I
Species
1
Base-changeevent
Bases atsite 1 foreach species
2 3 4 5 6 7
II
III
IV
I II III IV
Biochemical evidence (DNA Similarities) can be used instead of physical characteristics
LE 25-16
Lizard Bird Mammal
Four-chamberedheart
Mammal-bird clade
Lizard Bird Mammal
Four-chamberedheart
Four-chamberedheart
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
• Convergent evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages
D.5.6 Distinguish with example between analogous characteristics and homologous characteristics
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.5.10Discuss 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;
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