Mode of Inheritance

Mode of Inheritance is the manner in which a genetic trait or disorder is passed from one generation to the next. Autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, multifactorial, and mitochondrial inheritance are examples. Each mode of inheritance results in a characteristic pattern of affected and unaffected family members.3

Autosomal Dominant

Autosomal dominant inheritance refers to genetic conditions that occur when a mutation is present in one copy of a given gene (i.e., the person is heterozygous).3
Clinical Example: Hereditary Breast/Ovarian Cancer Syndrome associated with pathogenic variants in BRCA1, BRCA2, and PALB2 is a common example of an autosomal dominant genetic disorder.
Autosomal Dominant Inheritance Graphic

Autosomal Recessive

Autosomal recessive inheritance refers to genetic conditions that occur only when mutations are present in both copies of a given gene (i.e., the person is homozygous for a mutation, or carries two different mutations of the same gene, a state referred to as compound heterozygosity).3
Recessive Illustration

X-Linked Dominant

X-linked dominant inheritance refers to genetic conditions associated with mutations in genes on the X chromosome.3
Example: A single copy of the mutation is enough to cause the disease in both males (who have one X chromosome) and females (who have two X chromosomes). In some conditions, the absence of a functional gene results in the death of affected males.3

X-Linked Recessive

X-linked recessive inheritance refers to genetic conditions associated with mutations in genes on the X chromosome.3
Example: A male carrying such a mutation will be affected, because he carries only one X chromosome. A female carrying a mutation in one gene, with a normal gene on the other X chromosome, is generally unaffected.3

Mitochondrial

Mitochondria make most of the energy for the cell and have their own genetic material that is different from the genetic material found in the nucleus. Mitochondrial DNA is the small circular chromosome found inside mitochondria. The mitochondria, and thus mitochondrial DNA, are passed from mother to offspring.2,4
MItochondrial DNA Illustration


Subcategory - Family History

Pedigree

A graphic illustration of family history.2
Example: The pedigree shows the relationships between family members and indicates which individuals express or silently carry the trait in question.4
Pedigree Illustration

Proband

A proband is an individual being studied or reported on. A proband is usually the first affected individual in a family who brings a genetic disorder to the attention of the medical community.4