You can surely say that the overlap in a Ghanan and a Sami person's ancestry is quite small regarding recent millennia. But I don't see well defined groups at all. The reason it seems so in the US is because of the huge Western European (German/British) immigration early on and the large population of descendants of West African slaves. These two are sharply distinguishable (discounting for intermixing effects) but there are no "well defined groups" such as "black" and "white" when looking at it globally, not just in America. They are linked continuously via North/East Africans/Arabs/Turks and Mediterraneans.
Advice to not interpret any genetic data in a divisive manner here: http://www.ask-force.org/web/Golden-Rice/Yudell-Taking-Race-...
It's kind of like asking if Obama is really African American/Black. Races aren't sharply divided, it's a social grouping thing based on history, culture, etc.
Obama has clear facial features of a black person. This woman does not have them. She even looks like she got a perm just to look more black.
Let’s agree to disagree ;)
Race isn't straightforward.