Gene for Factor VIII. Hemophilia a is a hereditary bleeding disorder where there is a deficiency in clotting factor viii (factor viii is needed for blood clotting). It is inherited on the x-chromosome (sex-linked). Men only have 1 "x", so if their "x" is mutated, they will have the disease. Women have 2 "x's", so they can have 1 mutated "x" and 1 normal "x", and be a carrier of the disease, with mild or no symptoms.
Yes. Both hemophilia a and b are due to mutations in genes on the x chromosome.