For an autosomal dominant inherited disorder, what is the risk to each pregnancy?

• A. Males inherit the disorder with a greater frequency than females.
• B. Each pregnancy carries a 50% chance of inheriting the disorder.
• C. The disorders can occur in 25% of pregnancies.
• D. All children will be carriers of the disorder.

Answer: (B)

Autosomal dominant inheritance means one mutated allele is enough to cause the disorder. If one parent has one mutated allele and one normal allele (genotype Aa) and the other parent is unaffected (aa), each pregnancy has a 50% chance of inheriting the mutated allele and being affected, and a 50% chance of inheriting the normal allele and being unaffected. This risk is the same for males and females. The 50% figure is the standard risk in this typical scenario; it would be 100% only if the affected parent carried two mutated alleles, which is uncommon.