Charcot-Marie-Tooth Disease Type 1A (CMT1A / PMP22 Duplication) - Autosomal Dominant Pedigree

A 24-year-old architecture student presents with progressive distal weakness, bilateral foot drop, and characteristic "inverted champagne bottle" appearance of the lower limbs. Examination reveals bilateral pes cavus, hammer toes, atrophy of intrinsic hand muscles, absent ankle reflexes, and palpably thickened peroneal nerves. Nerve conduction studies show uniform slowing of motor and sensory nerves with motor conduction velocities of 22 m/s. A three-generation pedigree is shown with the proband marked. The inheritance pattern marked **A** in the diagram demonstrates which of the following key features?