5.4
cladistics
Essential Idea: The ancestry of groups of species can be deduced by comparing their base or amino acid sequences.
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Nature of Science: Falsification of theories with one theory being superseded by another: plant families have been reclassified as a result of evidence from cladistics.
UNDERSTANDINGS:
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5.4.U1 A clade is a group of organisms that have evolved from a common ancestor.
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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.
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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.
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5.4.U4 Traits can be analogous or homologous.
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5.4.U5 Cladograms are tree diagrams that show the most probable sequence of divergence in clades.
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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.
APPLICATIONS & SKILLS:
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Application: Cladograms including humans and other primates.
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Application: Reclassification of the figwort family using evidence from cladistics.
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Skill: Analysis of cladograms to deduce evolutionary relationships.
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RESOURCES: