Heterocromia means the characteristic somatic of individuals whose eyes have an iris of a different color from the other. In the case of different colors in the same eye is called somatic mosaicism.
The heterochromia is not a feature mostly human, but is often found in 5% of some animals such as dogs, cats (especially in the variety of the Turkish Van Van Kedi in which heterochromia is part of the genetic standard), the horse .
The heterochromia in human beings is a phenomenon that affects about 1% of people.
Usually both are identifiable characteristics from birth, although they may be acquired later in life. It was once believed that eye color depended on a single gene, but genetic studies have shown that eye color is polygenic, that is due to the interaction of several factors.