27th February 2024

Complications in inheritance

Mendelian inheritance refers to the inheritance of genetic disorders predominantly through the inheritance of a single gene. This can be through the autosomal or sexual chromosomes, leading to the four main classes of inheritance: autosomal dominant, autosomal recessive, X-linked dominant and X-linked recessive.

Genetic inheritance can be complicated by several factors, making the pattern of inheritance less clear:

• Pleiotropy – A single gene mutation results in phenotypes affecting multiple organ systems. This can result in one gene mutation presenting as seemingly unrelated symptoms.
• Penetrance – The degree to which a genotype is expressed towards an individual’s phenotype, resulting in some carriers not displaying the mutation’s phenotype.
• Variable expressivity – The degree to which a phenotype is expressed for a given genotype, resulting in different severity of symptoms between patients with a similar genotype.