« Reply #12 on: Monday 03 April 17 17:41 BST (UK) »
Specific chromosomes don't relate to population groups because we all have the same number of chromosomes. But of course matches can be used to track down a common ancestor, that's the reason a lot of us test. If two people have a significant match, such as the long strings on chr 2 and 17 that you mention, the likelihood is that those people are related. Gedmatch will give an idea of how many generations you might have to go back for the common ancestor. It's then a case of comparing trees, looking for a surname or location common to both and in the right generational window.
You still need to build your tree and do a bit of detective work, a DNA test isn't going to give it to you on a plate - "hi there, see me, the flashing green neon bit on chromosome 3? You and your DNA match inherited me from your great Uncle Albert twice removed" isn't reality yet.
Except when cousins marry, we each have two parents and four grandparents, eight GGP, 16 2xGGP, 32 3xGGP, 64 4xGGP etc. If gedmatch estimates (for instance) 4 generations difference you need to be looking at 3xGGP give or take a generation or two (because DNA inheritance isn't on an exact 50/50 basis). That's 32 surnames and locations. It helps a lot if you can at least tentatively "lop off" a branch, perhaps because the person you're trying to find the link with doesn't match other people for whom you've already found the common ancestor - that's why it's helpful to have known cousins test.
DNA testing for genealogical purposes isn't a magic bullet but it's a useful tool.
Jane :-)
ALLEN
BARR, BARRATT, BERRY, BRADLEY,BRAMLEY,BRISTOW,BROWN,BUGBIRD,BUTLER
CAIN,CARR,CHAPMAN,CHARLES,CH*LTON,CHESTER,COCKETT
COLLASON,COLLYER,CORKERY
DARLING, DENYER,DICKERSON,DOLLING,DURBAN
FARMER,FURNELL
GIBSON,GILES,GROOMBRIDGE
HALL,HAMBIDGE,HARMES,HART,HICKS,HILL,HOLLOWAY
JACKSON
K*AT*S
LANCASTER,LINTON
MCDONALD,MCFADEN,MEARS,MILLARD
NICOLAS,NOAK,NORTH
PARFIT,PORTER
RIPPINGALE,ROBINS
SEARLE,SPENCER,STEDHAM
TYLER,TILLY,TUCKWELL
WADE,WAGER,WALKER,WATSON,WEBB,WITHRINGTON,WOOD