What defines the condition known as hemophilia?

Hemophilia is a genetic disorder that specifically affects the body's ability to clot blood. The defining feature of hemophilia is the tendency to experience excessive bruising and prolonged bleeding even from minor injuries. This occurs due to deficiencies in specific clotting factors, which are proteins essential for the blood clotting process. When these factors are lacking or dysfunctional, the normal mechanism that stops bleeding is impaired, leading to spontaneous bleeding (often into joints and muscles) and difficulty in controlling bleeding during injury.

The other conditions mentioned, such as muscle degeneration, thick mucus production, and high blood pressure, are unrelated to hemophilia and describe completely different medical issues. Muscle degeneration is associated with disorders affecting muscle tissue, thick mucus production is characteristic of conditions like cystic fibrosis, and high blood pressure relates to cardiovascular health rather than coagulation. Thus, the hallmark symptoms of hemophilia are indeed excessive bruising and bleeding, making this the correct answer.