Marfan Syndrome (FBN1, Aortic Root Dilatation)

A 17-year-old male presents for pre-competitive sports screening with a height of 198 cm, arm span-to-height ratio of 1.08, arachnodactyly, pectus excavatum, and superotemporal ectopia lentis. Echocardiography shows aortic root dilatation (47 mm, Z-score 4.3) and mitral valve prolapse. His pedigree demonstrates **A: vertical transmission over four generations** with male-to-male transmission, both sexes equally affected, and early cardiovascular mortality from aortic dissection in relatives. Genetic testing confirms a heterozygous FBN1 pathogenic variant on chromosome 15q21. Which of the following inheritance patterns is definitively demonstrated by this pedigree feature?