Can a DNA test help prove a link?

[Braindead]

Hi. I'm completely new to the idea of DNA testing and wonder if it could prove a link in the following circumstances:
I am descended from my great great grandmother's second marriage but I'm not 100% certain of her first husband, although I think I have a pretty good idea. I know of descendants of her (presumed) first husband. If these people were also descendants of my g.g. grandmother, is there enough in a test to say, yes we are definitely related?
I'm sorry if this question is difficult to follow, and thanks in advance for any replies.

[medpat]

I had a DNA connection with a man who was a direct descendent of Richard, baptised 1702, brother of my 5th great grandmother Anne, baptised 1704. We therefore meet at our 6th gt grandparents born in the 1600s, We shared 17 cMs and are 7th cousins.

You could be 3rd cousins with the lady that's much nearer than my 7th cousin.

[Biggles50]

Yes(ish).

If the DNA match is of the same generation as you then the probability would be that they are a 1/2 Third Cousin and they would share about 50cM with you.

DNA is not always evenly passed down and in some cases a Grandparent may not pass any DNA down so a specific relationship can have a wide range of shared DNA.

Hence it is a case of ifs and buts.

Ideally other DNA matches who share the same Common Ancestor with you will come to light in time and if said matches upload to a comparison website like Gedmatch then Chromosome browsing and Triangulation tools could then be used to improve the probability of your hypothesis.

Good luck.

BTW if you have not yet tested your DNA then Ancestry is the one that Inwould suggest, they have 2x more tested customers than the next highest company and the Ancestry data can be uploaded to Gedmatch and My Heritage plus others whereas Ancestry does not accept uploads.

[Braindead]

Thanks for the replies, they're a great help.

[brigidmac]

I can answer your question with an example as I manage my nephew's DNA
He has 4 great grandparents who come from recomposed families ..ie that had children from first or second relationships

He matches descendants from great-great grandfather s first wife
and great grandmother s first husband
Plus mutual  descendants of the couple

And matches a descendant from  marriage of the other great great grandmother
 
But he does not match known descendant of a great great grandfather s half brother

[melba_schmelba]

Hi. I'm completely new to the idea of DNA testing and wonder if it could prove a link in the following circumstances:
I am descended from my great great grandmother's second marriage but I'm not 100% certain of her first husband, although I think I have a pretty good idea. I know of descendants of her (presumed) first husband. If these people were also descendants of my g.g. grandmother, is there enough in a test to say, yes we are definitely related?
I'm sorry if this question is difficult to follow, and thanks in advance for any replies.

To be more certain, ideally you need parents, grandparents, cousins or half siblings tested. If one or more of these close relatives on the line you are interested in also matches this more distant link, you can be more certain it isn't just a coincidental match.

[brigidmac]

I agree with Melba
Even if you have someone in younger generation ( ie nephew) who tests they could match a distant match  at a higher level

Once you have found a match you can look at all shared matches with them and group them into regions or surname matches .

[melba_schmelba]

I agree with Melba
Even if you have someone in younger generation ( ie nephew) who tests they could match a distant match  at a higher level

Once you have found a match you can look at all shared matches with them and group them into regions or surname matches .

Yes nieces and nephews too, and full siblings also. What may seem one of the many 100s of matches from 15-30cM on one sibling, can be 50-100cM on another and much more obviously a close match. The more cousins you have tested, the more likely it is you will be able to discover or confirm more distant parts of your tree.

[Braindead]

Thanks again for all the replies. One thing that comes across is that I really need to up my knowledge about what dna testing can or can't show.