Originally Posted by mrbean
But take the royal family, they thought that they needed to keep their blood clean, one had hemophelia, all the rest got it. It's highly unlikely that a person doesn't have a defect. It could be small and unnoticed for that person's life, but if they perform incest, the defect grows.
Hemophilia was a mutation in Queen Victoria, it hadn't existed before then. Also, since it's on the X chromosome, it had no effect on the women unless both of their parents passed on a recessive allele for the trait.