I must of read about this sometime in the past because I basically pulled this out of thin air (or my butt)
http://www.associatedcontent.com/article/2082253/are_the_cherokee_people_from_atlantis.html
“The Rh negative blood factor is recessive” — Rh factor is a second protein generated by a section on chromosome 9. Rh negative means the code isn’t there, and the protein doesn’t get produced. Assuming the main blood type considerations are taken into account, Rh positive people can receive Rh negative transfusions, but not the other way, if memory serves.