A cladogram is a type of graph that shows how closely related different types of organisms are in an evolutionary context. It resembles a tree, with various organisms being placed at the end of each branch. If two organisms have a close common branch, they are more closely related than those who have more distant branches. Since DNA, or corresponding protein sequences are more similar in closely related species, and more different in more distant species, a biologist can use those sequences to numerically determine how closely related three species are.