Royal wedding in Tonga unites & splits family

A royal wedding 'held recently in the Pacific island-state of Tonga has raised the centuries-old as well as universal concern about marriages between close relatives. 'Two prominent members of the royal family were reportedly absent from the big ceremony at a church on '12 July. In science, is there really a unique group of blood that predetermines a specific type of humans and their descendants to lord over others ?