Cladisitics
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. Skill: Analysis of cladograms to deduce evolutionary relationships. Theory of knowledge: • A major step forward in the study of bacteria was the recognition in 1977 by Carl Woese that Archaea have a separate line of evolutionary descent from bacteria. Famous scientists, including Luria and Mayr, objected to his division of the prokaryotes. To what extent is conservatism in science desirable? 
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An introduction to how life is related. Learn how phylogenetic trees are drawn. A must do activity!
Application: Reclassification of the figwort family using evidence from cladistics. Why were the organisms moved to different families? What evidence was used to reclassify them?
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