In autosomal dominant diseases:

• both homozygotes and heterozygotes manifest disease (there is no carrier state)
• both males and females affected
• only affected individuals can pass on disease
• disease is passed on to 50% of children
• normally appears in every generation (although see below)
• risk remains same for each successive pregnancy

Complicating factors:

• Reduced or non-penetrance: lack of clinical signs and symptoms (normal phenotype) despite abnormal gene. E.g. 40% otosclerosis
• spontaneous mutation: new mutation in one of gametes e.g. 80% of individuals with achondroplasia have unaffected parents