some people have a very hard time accepting that their genetics dont tie in with what they consider their own ethnicity to be
ultimately its a bit of a con
go back 10 generations and youve got 1000 ancestors to pick from, we also have ancestors that by chance/selection we inherit no DNA from, so mitochondrial(maternal lineage) and y-chromosomal(male) analyses can produce very different results
Its a confusing picture mt dna puts us all at sharing a common ancestor 200,000 years ago, y-chromo, 400,000 years ago, average automsomal about a million, the most recent genes we share we only acquired 3500 years ago
the other thing to consider is that genetic markers often dont correspond to geographic regions or even cultural or linguistic boundaries (even very inbred populations have some surprise genetic secrets)
In my first lab we studied families for rare diseases- 1 in 10 families would have a family member with genes that didnt come from the person they thought was their dad
basically as a race we move around a lot and shag around a lot more than people realise, it takes <1month to walk from britain to africa, in theory you could make a lot of babies on your way!