A 6-year-old boy is brought to the pediatric clinic with bowed legs, short stature, and dental caries. His father is similarly affected with rickets refractory to standard vitamin D therapy. On pedigree analysis, the boy's paternal grandfather is affected, but the paternal grandmother is unaffected. Notably, ALL of the paternal grandfather's daughters are affected, while NONE of his sons are affected. The structure marked **A** in the pedigree diagram represents this pathognomonic inheritance pattern. Which of the following inheritance patterns does this pedigree MOST strongly suggest?