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5.4 Cladistics

IB Syllabus Statements

Understandings:

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

  • 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.

  • 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.

  • Traits can be analogous or homologous.

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

  • 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 and skills:

  • Application: Cladograms including humans and other primates.

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

  • Skill: Analysis of cladograms to deduce evolutionary relationships.

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Cladistics

Reclassification of Figworts

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Topic 5.4 Cladistics HookED SOLO Hexagons

  • Explain what ‘falsification of theories’ means and why this would happen.

  • Define clade.

  • What kind of evidence is used to determine which species are included in a clade.

  • Outline the relationship between the number of base sequence differences between two species and the time since they diverged from a common ancestor.

  • Compare analogous vs. homologous traits.

  • What are cladograms and what are they used for?

  • Explain how classifying organisms based on cladistics can be more useful than classifying organisms based on morphological features.

  • Explain what you would expect to see on a cladogram that includes humans and other primates.

  • Outline the reclassification of the figwort family using evidence from cladistics.

  • Explain how you would use a cladogram to deduce evolutionary relationships.

  • How can the ancestry of groups of species be deduced?

Topic 5.4 Cladistics SSaQ (Syllabus Statement as Questions)

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