Autosomal Dominant Inheritance

Autosomal dominant inheritance is a Mendelian pattern in which a single altered copy of a gene on an autosome (a non-sex chromosome) is sufficient to produce the trait or disorder. Affected individuals are typically heterozygous, and on average half of their children inherit the variant, giving the characteristic 'vertical' transmission seen across successive generations in a pedigree.

Definition

Autosomal dominant inheritance is transmission of a trait determined by a single copy of an allele at an autosomal locus, so that heterozygous individuals are affected and, on average, transmit the allele to half of their offspring regardless of sex.

Scope

The entry covers how dominant autosomal alleles behave, the expected pedigree features and recurrence probabilities, and the molecular reasons one mutant allele can suffice (such as haploinsufficiency or dominant-negative and gain-of-function effects). It also notes complicating phenomena — new mutations, mosaicism, and reduced penetrance — that make real pedigrees depart from the textbook pattern. It is a conceptual reference, not clinical counselling.

Core questions

• What pedigree features distinguish an autosomal dominant pattern from recessive or X-linked patterns?
• Why is one altered allele enough to produce a phenotype, and through what molecular mechanisms?
• How do new mutations, mosaicism, and incomplete penetrance complicate the expected dominant pattern?

Key concepts

• Heterozygous affected individuals
• Vertical (generation-to-generation) transmission
• Equal transmission to both sexes
• Haploinsufficiency
• Dominant-negative effect
• Gain-of-function mutation
• De novo mutation and parental mosaicism
• Male-to-male transmission (excludes X-linkage)

Mechanisms

A dominant phenotype appears when one mutant allele disrupts function despite a normal allele on the homologous chromosome. This can occur through haploinsufficiency (a single functional copy provides too little gene product), a dominant-negative effect (the abnormal product interferes with the normal one, common in multimeric proteins), or a gain of function (the altered product acquires a new or constitutive activity). Because the locus is autosomal, males and females are affected equally and an affected parent transmits the allele to each child with a one-half probability; male-to-male transmission, which cannot occur for X-linked traits, is a useful confirming feature. Many dominant disorders also arise as de novo mutations, and apparent skipping of generations may reflect reduced penetrance rather than non-inheritance.

Clinical relevance

Identifying a dominant pattern frames how recurrence is reasoned about in a family and signals that an affected individual's first-degree relatives may share the variant. This material describes the inheritance concept for reference; it does not provide individualized risk figures, testing recommendations, or counselling, which require formal clinical genetic evaluation.

Epidemiology

Dominant disorders are individually uncommon but collectively numerous within the catalogue of Mendelian conditions. A notable feature is that a substantial proportion of cases for some severe dominant disorders arise from new mutations in the affected individual, so an affected child may have unaffected parents.

History

The dominant/recessive distinction originates in Mendel's 1866 crosses, in which one trait masked the other in heterozygotes. With the rediscovery of Mendel's work and the cataloguing of human phenotypes through the twentieth century, autosomal dominant transmission became one of the standard inheritance modes recorded for thousands of single-gene conditions.

Key figures

• Gregor Mendel
• Victor McKusick

Seminal works

• mendel-1866
• nussbaum-2016

Frequently asked questions

If a disorder is autosomal dominant, what is the chance an affected parent passes it to a child?

For a heterozygous affected parent, each child has on average a one-half chance of inheriting the allele, and the chance is the same for sons and daughters because the locus is on an autosome; penetrance and other factors then influence whether an inheritor is clinically affected.

Can a child have an autosomal dominant disorder when neither parent is affected?

Yes — this commonly reflects a de novo (new) mutation arising in the egg, sperm, or early embryo, and less often parental gonadal mosaicism or reduced penetrance in a parent.