The study of human genetic characteristics presents some major obstacles. First, controlled matings are not possible. With other organisms, geneticists can carry out specific crosses to test their hypotheses about inheritance. Unfortunately (for geneticists at least), matings between humans are more frequently determined by romance, family expectations, and—occasionally—accident than by the requirements of geneticists. Other obstacles are the long generation time and generally small family size of our species. To overcome these obstacles, geneticists have developed special techniques for studying human inheritance that are uniquely suited to human biology and culture.

One technique used by geneticists to study human inheritance is the analysis of pedigrees. A pedigree is a pictorial representation of a family history, essentially a family tree that outlines the inheritance of one or more characteristics. When a particular characteristic or disease is observed in a person, a geneticist often studies the family of this affected person by drawing a pedigree.