"Hemophilia is an genetic bleeding disorder, affecting mostly males, that prevents blood from forming an effective clot" (qtd. in "Hemophilia Encyclopedia"). Hemophilia comes from the Latin word hemo, meaning blood, and philia meaning love. Blood in a person that does not have hemophilia contains proteins that act as clotting factors to stop bleeding. Hemophiliacs are either missing these clotting factors or the clotting factors are not working properly ("Hemophilia - a Timeline"). .
There are three different levels of severity of hemophilia: mild, moderate, and severe ("Hemophilia - a Timeline"). The level of severity corresponds with the amount of clotting factor present in the blood ("Hemophilia"). The level of severity a hemophiliac is born with does not change with time, i.e., a person born with a moderate case of hemophilia will not develop severe hemophilia ("Hemophilia Encyclopedia"). .
There are two types of hemophilia: hemophilia A and hemophilia B. Persons with hemophilia A have a factor VIII deficiency, and persons with hemophilia B have factor IX deficiency. People are much more likely to have hemophilia A than hemophilia B. Because it is the most common of the factor deficiencies, hemophilia A is also known as "Classical hemophilia" ("Hemophilia Encyclopedia"). .
The gene for hemophilia is found on the X chromosome. Women are carriers of the disease. "A carrier is a person who has a defective gene for a certain trait, such as hemophilia, but who does not exhibit that trait" (qtd. in "Hemophilia Encyclopedia"). Males have one X chromosome and one Y chromosome, while females have two X chromosomes. In this fact lies the reason why hemophilia in women is rare. While one of the X chromosome in a female may contain a nonfunctional clotting factor gene, her other X chromosome will usually compensate for the lack of or nonfunctionality of the clotting factor. Males, on the other hand, have only one X chromosome.