Autosomal dominant
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What it means
One mutant allele suffices; ~50% of offspring affected; vertical transmission through generations, both sexes. Variable penetrance/expressivity common. Examples: Huntington, NF1/2, Marfan, ADPKD, familial hypercholesterolaemia, HHT, hereditary spherocytosis, BRCA, FAP, MEN, tuberous sclerosis, achondroplasia.
Worked example
An affected parent, affected child in each generation, no skipping, and roughly equal sons and daughters → autosomal dominant.
In the exam
A pedigree shows the trait in every generation, passed from an affected parent to about half the children of both sexes, with no skipped generations.
What settles it
AD = every generation (vertical); AR = skips generations with unaffected carrier parents (horizontal clustering in sibs).
Classically confused with
Autosomal recessive
Source: StatPearls