Hemophilia B: Hemophilia due to deficiency of coagulation factor IX in the blood, which results in prolonged oozing after minor and major injuries, tooth extractions, or surgery. There is renewed bleeding after the initial bleeding has stopped. The gene for hemophilia B is on the X chromosome, so males are affected and females carry the gene. About 10 percent of carrier females are at risk for bleeding. Treatment involves administration of blood products that introduce clotting factor IX and replace lost blood. Also called Christmas disease (named for the first patient with the disease to be studied in detail).