Inheritance Patterns

Definition

Describes how a genetic condition is passed on within a family. There are five main patterns:

How it is passed on: A single altered copy of the gene in each cell is enough for the person to be affected.
Who is affected: Everyone with a single mutant copy shows symptoms
Carrier status: Not applicable; a person with a single copy is not a carrier but affected
Examples: Huntington disease, Marfan syndrome

How it is passed on: For the condition to appear, both copies of the gene must carry a variant
Who is affected: Only those with two mutant copies show symptoms
Carrier status: Each parent of an individual with an autosomal recessive condition carries one copy of the altered gene, but they typically do not show symptoms.
Examples: Cystic fibrosis, sickle cell anemia
In the context of Turkey/Cyprus: In communities where consanguineous marriage is relatively common, autosomal recessive diseases are seen more frequently, and the importance of carrier screening increases here

How it is passed on: A variant in a single gene on the X chromosome causes disease in males; in females a single affected copy is enough
Who is affected: All males carrying the variant and females with a single variant copy
Carrier status: Females with a single variant may experience milder symptoms than males
Example: Fragile X syndrome

How it is passed on: In males a single mutant copy is enough; in females two copies are required
Who is affected: Predominantly males; males are affected by X-linked recessive disorders far more often than females
Carrier status: Heterozygous females (a single variant copy) are typically unaffected carriers
Example: Hemophilia

How it is passed on: Only females can pass mitochondrial variants to their children, because the egg cell supplies the mitochondria to the embryo
Who is affected: Both males and females across generations
Carrier status: Fathers do not pass these disorders to their children
Example: Leber hereditary optic neuropathy (LHON)