Explain why scientists use shared characteristics to make cladograms.

 Scientist use synapomophies, or shared derived characters, to define cladograms. For instance, mammary glands are a shared characteristic of mammals. All mammals and their oldest common ancestor, had or have mammary glands.Thus, if we are looking at an unidentified animal and trying to place it in a cladogram, if it has mammary glands we know it belongs in that branch. Cladogram is a diagram used to represent a hypothetical relationship between groups of animals, called a phylogeny. A cladogram is used by a scientist studying phylogenetic systematics to visualize the groups of organisms being compared, how they are related, and their most common ancestors.  

Sample Response: Shared characteristics are features or qualities that organisms have in common with each other. They are used to make cladograms because they show the relationships among organisms. They can also show which organisms have a common ancestor.