5.4 Cladistics

Essential Idea

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

Understandings

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

2. 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.

3. 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.

4. Traits can be analogous or homologous.

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

6. 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.

Applications

1. Cladograms including humans and other primates.

2. Reclassification of the figwort family using evidence from cladistics.

Skills

1. Analysis of cladograms to deduce evolutionary relationships.

Guidance

• None

Key Vocabulary

• Cladistics

• Cladogram

• Clade

  • Common ancestry

    • Base sequence (of a gene)

    • Amino acid sequence (of a protein)

• Traits

  • Analogous

  • Homologous

• Reclassification

Textbook Reading and/or Activities

Click HERE for a pdf of chapter 5.

• Pages 270-283

  • Nature of Science (p.270)

  • Worked Example (p.276)

  • TOK (p.279)

  • Nature of Science (p.279)

  • Worked Example (p.279-280)

  • Exercises (p.281)

  • Practice Questions (p.282-283)

Notes and Study Questions

Bob Smullen Notes Study Questions

Jacob Cedarbaum Notes Study Questions

Stephen Taylor Notes Study Questions

Chris Paine Notes Study Questions

Learning Activities

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Supplemental Reading

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