There are hundreds of genetic disorders that plague millions of people all around the world. One of these disorders is hemophilia, a mutation of the X chromosome that severely reduces the necessary factors used to clot human blood. Hemophilia was discovered in the Tenth Century by medical scholer Abulcasis, when he observed grown men in the army die of severe blood loss after sustaining only minor cuts and abrasions. Later, in 1803, John Conrad Otto, a Philadelphian physician, noted that, in certain families, the males suffered from unstopping bleeding from small wounds. Otto classified these people “bleeders” due to the fact that their blood appeared not to clot. Finally, in 1828, Friedrich Hoff, a student at the university of Zurich, classified this disease as haemorrhaphilia so that it could be classified on scene by first responders. The term we use today, “hemophilia”, is derived from this early classification. Hemophilia is a rare disorder, affecting only 1 in 10,000 births. When compared to down syndrome, the most common genetic disorder, hemophilia is 15 times rarer than down syndrome. This is why hemophilia is almost never calcified at birth, but only after about 2 years is hemophilia diagnosed. Some of the most common symptoms of hemophilia are, easy bruising, frequent bloody noses, and severe joint pain caused from blood leaking into the joints. Now that we know what hemophilia is, we can explore how it happens. Hemophilia is a mutation of the X chromosome in a human. In meiosis, when sex cells are reproduced, the sperm cell either gets the males X chromosome or his Y chromosome. The egg cell however, is guaranteed to have an X chromosome because the female has two X chromosomes and no Y chromosome. For this reason, there is a 50% chance that the female carrier of the mutated gene will pass it to her son or daughter. However, if the male is the carrier, he is guaranteed to pass on his mutated X chromosome to his daughters, but cannot pass it to his son. This is because that for a daughter to be born, the male has to pass on his duplicated X chromosome so that the child will have two X chromosomes. For a son to be born however, the father has to pass his Y chromosome to the child, not his X chromosome, so that the child will have one X and one Y chromosome.