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;