Final answer:
Hemophilia, referred to as "the royal disease," is a genetic disorder characterized by a deficiency of clotting factors in the blood, leading to prolonged and potentially life-threatening bleeding events. It is most well-known for affecting the male descendants of European royalty, such as Queen Victoria's lineage.
Step-by-step explanation:
The hereditary blood defect known as "the royal disease" is hemophilia. Hemophilia is a genetic disorder where there is a deficiency or absence of certain clotting factors in the blood, which are normally released by platelets to help stop bleeding. Individuals with hemophilia can experience prolonged bleeding from any cut or injury, as well as dangerous internal bleeding, often into muscles and joints.
This disease became notoriously associated with the royal families of Europe, most famously affecting the male descendants of Queen Victoria. Hemophilia A and B are the most common forms, with hemophilia A being caused by a deficiency of factor VIII, and hemophilia B (also known as Christmas disease) resulting from a deficiency of factor IX.
As a sex-linked recessive disorder, typically, males are affected while females are carriers of the gene. The significance of the disease in the royalty of Europe gave rise to its nickname as the royal disease.