Sex-Limited Inheritance — Androgenetic Alopecia

A 35-year-old Indian male presents with progressive bitemporal hair recession and vertex thinning over the past 10 years. His father and paternal grandfather were both bald, but his mother and maternal grandmother have full scalp hair despite carrying the same allele. Genetic testing confirms an autosomal dominant susceptibility variant. The inheritance pattern shown in the pedigree is marked as **A** in the diagram. Which of the following BEST explains why this trait is expressed in males but NOT in females who carry the same allele?