Hemophilia is a rare bleeding disease that is carried on the X-chromosome. More than 400,000 people worldwide live with this disease, 20,000 of those within the United States. It is commonly called the “royal disease” because Queen Victoria was known to be a carrier of the disease and passed the gene to other members of the royal family.


If a healthy individual who does not have hemophilia gets a small cut on their arm, it takes 2-8 minutes on average for clotting to occur and for the bleeding to stop. People suffering from hemophilia lack an essential blood-clotting protein in their blood plasma. If they get cut, it can take 30 minutes to 22 hours for the bleeding to stop. Excessive bleeding is a constant danger to individuals with hemophilia.


Figure 1 shows the pedigree of hemophilia in four generations of Queen Victoria’s family.



Based on the information provided, which of the following statements is true about the 400,000 people living with hemophilia?