Analysis of Cladograms
Analyzing a Cladogram
The first step in basic cladistic analysis is to determine which character states are primitive (old) and which are derived (new). The outgroup comparison method is the most common method of analysis. In outgroup comparison, if a taxon that is not a member of the group of organisms being classified has a character state that is the same as some of the organisms in the group, then that character state can be considered to be primitive or plesiomorphic. The outside taxon is called the outgroup and the organisms being classified are the ingroup.
The only way a homologous feature could be present in both an ingroup and an outgroup, would be for it to have been inherited by both from an ancestor older than the ancestor of just the ingroup.
The first step in basic cladistic analysis is to determine which character states are primitive (old) and which are derived (new). The outgroup comparison method is the most common method of analysis. In outgroup comparison, if a taxon that is not a member of the group of organisms being classified has a character state that is the same as some of the organisms in the group, then that character state can be considered to be primitive or plesiomorphic. The outside taxon is called the outgroup and the organisms being classified are the ingroup.
The only way a homologous feature could be present in both an ingroup and an outgroup, would be for it to have been inherited by both from an ancestor older than the ancestor of just the ingroup.
How to construct your own cladogram
Monophyletic group - Includes all descendants of a common ancestor Paraphyletic group - Contains only some descendants of the common ancestor Polyphyletic group - Does not contain the common ancestor at all |