Hereditary Multiple Exostoses EXT1 Autosomal Dominant

A 12-year-old boy presents with multiple firm bony prominences on both knees, wrists, ankles, and shoulders that have progressively increased since age 4. His father, paternal grandfather, older brother, and younger sister are all similarly affected. His paternal grandfather underwent amputation for chondrosarcoma arising from a femoral exostosis. The pedigree pattern shown in the diagram is marked as **A**, demonstrating vertical transmission through three generations with male-to-male transmission and both sexes affected. Which of the following inheritance patterns best describes the genetic basis of this condition?