Which features can we use to arrange species into "family trees" of related species?

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What is a cladogram and what does it tell us about the relationships between organisms?

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5.4 Cladistics

The ancestry of groups of species can be deduced by comparing their base or amino acid sequences.

5.4 Cladistics

Essential idea

5.4 Cladistics

5.4 Cladistics

What is a clade?

5.4.U1 A clade is a group of organisms that have evolved from a common ancestor.

• Cladistics uses cladograms
• Shows clades (branches) that begin at a node
• Each clade contains a common ancesteral organism
• Members of a clade share dervived characteristics
• Clades are subsets of large clades
• Cladograms show evolutionary history
• Branch length can indicate time
• Based on molecular analysis (DNA, Amino Acids) and genetic evidence
• Fewest number similarities = branch
• Predictability of origin
• Non-Linnean

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5.4 Cladistics

What is cladistics?

5.4 Cladistics

Syllabus Reference

Species may evolve over time to form a new species. Consequently there are groups of species derived from a common ancestor. Such groups are called Clades.

5.4 Cladistics

What is a clade?

5.4.U1 A clade is a group of organisms that have evolved from a common ancestor.

Cladograms are mostly based on DNA base sequences or the amino acid sequences in a protein.

The branching points on cladograms are called nodes.

Nodes denote a speciation event when a common ancestor splits into two, or more, species.

5.4 Cladistics

A cladogram is a tree diagram showing the similarities and differences between different species

5.4.U5 Cladograms are tree diagrams that show the most probable sequence of divergence in clades.

An example cladogram

5.4 Cladistics

5.4 Cladistics

Building a Cladogram

5.4 Cladistics

The DNA evidence used to build this cladogram of primates, including humans. can also be used to estimate when species diverged and hence when the common ancestor existed.

5.4 Cladistics

5.4.A1 Cladograms including humans and other primates

5.4.U3 Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.

Amino Acid Sequence of Certain Proteins

• The sequences for alpha and beta hemoglobin are known for humans, chimpanzees, and gorillas. Humans and chimpanzees have identical alpha and beta sequences from which gorillas differ by only one residue in each chain.
• On position 23 on the alpha hemoglobin, for example, gorillas have the amino acid aspartic acid instead of glutamic acid and at position 104 on beta hemoglobin gorillas have lysine instead of arginine.
• Link on similarities between human and chimpanzee DNA http://bit.ly/1DXeU0N
• Scientific American Article http://bit.ly/1HkmRwt

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5.4 Cladistics

Check this out!

5.4.U2 Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.

• The majority of organisms on earth use left-handed amino acids to build their proteins and only a small number use right-handed amino acids (mostly certain bacteria). This implies common ancestry for these life forms with the same amino acid orientation

5.4 Cladistics

Amino acids also have either right-handed or left-handed orientation

What is a cladogram?

5.4 Cladistics

Work through the first 6 pages of this interactive and complete the worksheet here:

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https://evolution.berkeley.edu/evolibrary/article/evo_04

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Candy Cladograms

1. Select 6 different sweets from the Haribo packet.
2. Using the information in the video arrange them into a cladogram.
3. At each stage add the identifying feature that the organisms have in common
4. Take a photograph!
5. Now select an additional sweet to represent the discovery of a new organism.
6. Where does it go on your cladogram and why?

5.4 Cladistics

Analogous and Homologous Features

5.4 Cladistics

Homology - traits inherited by two different organisms from a common ancestor

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5.4.U4 Traits can be analogous or homologous.

Butterfly wing

Bird wing

5.4 Cladistics

Analogy - similarity due to convergent evolution, not common ancestry

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5.4.U4 Traits can be analogous or homologous.

Learn more here!

5.4 Cladistics

What are some examples of how classification of organisms has changed in the light of evidence from cladistics?

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5.4 Cladistics

5.4.A2 Reclassification of the figwort family using evidence from cladistics.

Figworts, what we need to know:

Understandings: Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.

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Application: Reclassification of the figwort family using evidence from cladistics.

Nature of science: Falsification of theories with one theory being superseded by another—plant families have been reclassified as a result of evidence from cladistics

5.4 Cladistics

5.4 Cladistics

Learn more about the reclassification of Figworts here!

5.4.A2 Reclassification of the figwort family using evidence from cladistics.

Application: Reclassifying Figworts

Originally scientists classified organisms using their observable features.

New data from DNA and amino acid sequences has led to evidence which disputes some of the original classification of organisms.

One example of this is the plant genus Scrophularia also known as Figworts

5.4 Cladistics

5.4.U6 Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.

Reclassifying Figworts

Group them according to their observable features and build a cladogram using this information.

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5.4 Cladistics

Look at the images of the Figwort family.

5.4.A2 Reclassification of the figwort family using evidence from cladistics.

5.4 Cladistics

5.4.A2 Reclassification of the figwort family using evidence from cladistics.

5.4 Cladistics

New DNA evidence classifies the Figworts very differently as you can see from this cladogram:

5.4.A2 Reclassification of the figwort family using evidence from cladistics.