A pattern of genetic inheritance in which only one copy of a particular gene needs to be present for a trait (such as brown eyes) to be expressed; though a person may carry two genes for the same dominant trait, only one is needed. Among the genetic disorders that are of the autosomal dominant type are achondroplasia, Huntington’s chorea, Polydactyly, and neurofibromatosis. A disorder may affect individuals in widely varying ways; some may show mild signs of a disease, while others may have a severe form of the disorder. Even if a child is not seriously affected, it is important to diagnose a mild form of the disorder, to help prevent damage from later possible effects and also to help parents and their genetic counselors judge the likelihood that another child may be seriously affected.