A 22-year-old woman presents with progressive bilateral sensorineural hearing loss, tinnitus, and vertigo. MRI brain shows bilateral vestibular schwannomas, a falcine meningioma, and a spinal ependymoma. Genetic testing confirms NF2 mutation. Her pedigree is shown in the diagram. The pattern marked **A** (vertical transmission across three generations) is most consistent with which inheritance pattern and which gene is responsible?