1. Phylogeny and classification
D.5.5-D.5.10
Phylogeny and classification

2. Linking Classification and Phylogeny
Evolutionary relationships in branching phylogenetic trees -- Called a cladogram

3. LE 25-9 Panthera pardus (leopard) Mephitis mephitis (striped skunk)
Lutra lutra
(European
otter)
Canis
familiaris
(domestic dog)
Canis
lupus
(wolf)
Species
Genus
Panthera
Mephitis
Lutra
Canis
Family
Felidae
Mustelidae
Canidae
Order
Carnivora

4. Cladogram
Each branch point represents the divergence of two species

5. Evolutionary Relationships/ phylogeny is depicted in an evolutionary tree/ cladogram
Evolutionary relationships in branching trees

6. Evolutionary Relationships/ Phylogeny is depicted in an Cladogram
Nodes show that groups share a common ancestor & evolved from this ancestor

7. Evolutionary Relationships/ Phylogeny is depicted in an Cladogram
Each branch point represents the divergence of two species
Branching

8. Evolutionary Relationships/ Phylogeny is depicted in an Cladogram
Carnivora
Panthera
pardus
(leopard)
Mephitis
mephitis
(striped skunk)
Lutra lutra
(European
otter)
Canis
familiaris
(domestic dog)
lupus
(wolf)
Species
Genus
Family
Order
Felidae
Mustelidae
Canidae
Lutra
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

9. How many common ancestors does G and H have?
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.

10. 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

11. Evolutionary Trees/ Phylogenies also show relative time.
The top of the tree being more recent.
The bottom showing the distant past

12. 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

13. 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.

14. 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;

18. A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants

19. LE 25-10a
Grouping 1
Monophyletic

24. A monophyletic group = CLADE

33. D.5.7 Outline methods to construct cladograms and the conclusions that can be drawn from them
How cladograms are made
Make a list of all the organisms which will be included in your cladogram
List the characteristics each organism possesses

34. Then you make a table like the one below:
D.5.7 Outline methods to construct cladograms and the conclusions that can be drawn from them: How cladograms are made
Once the list is made the characteristics common to all organisms this trait is considered a primitive trait.
Then you make a table like the one below:
Multicellular
Vertebral column
Hair
placenta
total
sponge ✓ x 1
sailfish 2
wombat 3
elephant 4

35. STEP 5: USE DATA TABLE TO CONSTRUCT A VENN DIAGRAM

36. STEP 6. CONVERT VENN DIAGRAM TO A CLADOGRAM

40. 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

41. Organisms at the bottom are the earliest ones
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.
Drosophila
Lancelet
Fish
Amphibian
Bird
Human
Rat
Mouse
Cenozoic
Mesozoic
Paleozoic
65.5
251
542
Neoproterozoic
Millions of
years ago

42. Human
Mushroom
30%
Tulip
40%
Percentage differences between sequences
Comparison of possible trees
15%
20% 5%
10%
25%
Tree 1: More likely
Tree 2: Less likely
Biochemical evidence (DNA Similarities) can be used instead of physical characteristics

43. LE 25-15ab
Sites in DNA sequence 1 2 3 4 5 6 7
Biochemical evidence (DNA Similarities) can be used instead of physical characteristics I II
Species
III IV I II
III IV
Bases at
site 1 for
each species
Base-change
event

44. LE 25-16 Lizard Bird Mammal Four-chambered heart Mammal-bird clade
Lizard-bird clade

45. 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

46. 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

51. 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.

52. IB Practice Test Question 1
Define the term clade. (1)

53. 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

54. IB Practice Test Question 2
Suggest two reasons for using cladograms for the classification of organisms.(2)

55. 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;

56. IB Practice Test Question 3
Using examples, distinguish between analogous characteristics and homologous characteristics.(4)

57. 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.

58. 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)

59. 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;

60. IB Practice Test Question 5
Outline the evidence provided by DNA for the common ancestry of living organisms. (2)

61. 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;

62. 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;