Source: Hillman RS, et al. (2005). Hemophilia and other intrinsic pathway defects. In RS Hillman et al., eds., Hematology in Clinical Practice, 4th ed., chap. 32, pp. 368–379. New York: McGraw-Hill.

• If the father has hemophilia and the mother is a carrier, sons will have a 50% chance of having hemophilia. Daughters will have a 50% chance of having hemophilia and a 50% chance of being a carrier. It is very rare for both parents to have these defective genes.
• If the father does not have hemophilia and the mother is a carrier, sons will have a 50% chance of having hemophilia. Daughters will have a 50% chance of being carriers.
• If the father has hemophilia and the mother has normal blood, all sons will be normal and all daughters will be carriers.
• About 33% of hemophilia occurs spontaneously when a normal chromosome changes (mutates).