Cladograms are used to show evolutionary relationships among organisms. A cladogram consists of a line with Y-shaped branches or forks. Each branch is labeled with a special characteristic that separates the organisms to the right of the label from the organisms on the left.
Pick organisms to include in the cladogram
Cladograms generally consist of members of the same order or family. For example, the cladogram may trace the evolution of members of the canine family. This group of organisms is called the ingroup. The first organism on the cladogram, called the outgroup, may be a member of another order or family for comparison.
Determine the characteristic that differentiates the ingroup from the outgroup
Compare the characteristics of the ingroup against the outgroup. Identify one characteristic that makes them different. Draw a horizontal line across a piece of paper. Leaving enough space for a branch to the left, make a small mark across the line and record the differing characteristic below the mark. Place the outgroup on a branch coming off the top of the horizontal line to the left of the characteristic. All members of the ingroup are placed on branches coming off the top of the line to the right of this characteristic.
Determine how the members of the ingroup are different
Analyze the characteristics of the ingroup. Place the characteristics in evolutionary order from left to right on the cladogram. Organisms branch off the main line to the right of any characteristic which they possess.