Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Hemophilia ?
    ### Response:
    A defect in one of the genes that determines how the body makes blood clotting factor VIII or IX causes hemophilia. These genes are located on the X chromosomes (KRO-muh-somz).
                
Chromosomes come in pairs. Females have two X chromosomes, while males have one X and one Y chromosome.
    