Hemophilia A — X-Linked Recessive with Carrier Daughter

A 6-year-old boy presents with recurrent hemarthroses of the right knee and prolonged bleeding after minor dental extraction. Factor VIII activity is 2% of normal. His maternal uncle and maternal grandfather also had lifelong bleeding disorders. The pedigree diagram (marked **B**) shows only males affected, transmission through phenotypically unaffected females, and no father-to-son transmission—diagnostic of X-linked recessive inheritance. The proband's mother is an obligate carrier. If this affected boy has children with an unaffected woman, what is the probability that his daughters will be carriers of hemophilia A?