Autosomal dominant inheritance has surviving affected individuals, in a heterozygous state. In X linked mental retardation the X chromosome shows a fragile site at the tip of its short arm. Familial hypercholesterolaemia is autosomal dominant. Alpha thalassemia is autosomal recessive. Adult polycystic kidney disease is autosomal dominant.
Hurler syndrome is autosomal recessive.
Sickle cell anaemia is inherited as an autosomal dominant condition. Most isolated neural tube defects belong to this category. The recurrence risk in his type, does not depend on the previous incidence of the same condition in the family. Blood groups are inherited in this manner. It is due to the effects of a large number of genes and the environment.