Final answer:
Hemophilia A is the most common mild bleeding disorder, while von Willebrand disease is the most common severe bleeding disorder.
Step-by-step explanation:
The most common mild bleeding disorder is hemophilia A, accounting for approximately 80 percent of cases. It is a genetic disorder that results in the inability to synthesize sufficient quantities of factor VIII, a clotting factor. Hemophilia B, which is a deficiency of factor IX, is the second most common form, accounting for approximately 20 percent of cases. Both of these forms of hemophilia are linked to the X chromosome and are typically passed from a carrier mother to her male offspring.
On the other hand, the most common severe bleeding disorder is von Willebrand disease, which affects the ability of blood to clot. It is caused by a deficiency or dysfunction of von Willebrand factor, a protein that helps platelets stick together and form clots. This disorder is typically inherited in an autosomal dominant manner, meaning that individuals with a single copy of the defective gene are affected.