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