Wikipedia to the help: http://en.wikipedia.org/wiki/Three-parent_baby:
Three-parent babies are human offspring with three genetic parents, created through a specialized form of In vitro fertilisation in which the future baby's mitochondrial DNA comes from a third party.
See also http://www.bbc.com/news/magazine-28986843 for the young case of Mrs. Saarinen.
Such a child would have DNA from three people. If one genetic source would be a 100% cherokee and others 0% cherokees, he or she would be 1/3 cherokee. Her/his offspring would be 1/6 cherokee and subsequent offpring 1/12 cherokee provided later parents were 0% non-cherokees.
All this is assuming rather loose-minded mathematical reasoning or simplistic reductionism of complexities of genetics.