Types of inheritance of genetically determined diseases

There are three main types of inheritance of genetically determined diseases: autosomal dominant, autosomal recessive and sex-linked.

Autosomal dominant inheritance means that a single copy of a mutated gene is sufficient to develop a disease. If one parent has an autosomal dominant disease, each of their children has a 50% chance of inheriting the disease.

Autosomal recessive inheritance means that two copies of the mutated gene are needed to develop the disease. If the parents do not have the disease, but are both carriers of the mutated gene, then each of their children has a 25% chance of inheriting the disease.

Sex-linked inheritance means that the gene responsible for the disease is located on one of the sex chromosomes. There are two types of sex-linked inheritance:

• X-linked dominant inheritance means that a single copy of the mutated gene located on the X chromosome is enough to develop the disease. Men who have X-linked dominant disease always get the disease. Women with X-linked dominant disease can be carriers or sick.
• X-linked recessive inheritance means that two copies of a mutated gene located on the X chromosome are needed to develop the disease. Men who have X-linked recessive disease are always sick. Women who have X-linked recessive disease can be carriers or sick, but are usually carriers.
• Y-chain inheritance means that the gene responsible for the disease is located on the Y chromosome. Thus, the disease is only found in males.