Mood disorders are conditions that go beyond an occasional “bad day” into the realm of severe emotional disturbance. Mood disorders include depression (the most common mood disorder), bipolar disorder, and schizophrenia. By examining family medical histories and adoption studies, researchers have concluded that bipolar illness and genetics are linked. However, the presence of certain gene sequences is not a mandate, as only about 60 percent of monozygotic (“identical”) twins with the bipolar sequence actually become ill. It is obvious that environmental and societal factors also play roles in determining one’s mood.