Eliminating lines through DNA

This may seem a basic question but I would like confirmation from more informed sources than my own guesswork as I seem to be going round in circles. At night, in bed, I am convinced I have it sussed but when looking at it in the cold light of day, I am mistaken.

I have identified a very close line to me, my sister and nephew (brother's son) which did not feature in my tree before my dna test. As it is so significant, I have to assume that one of my researched lines is not a genetic line. Therefore I am going through the very slow process of identifying matches to my tree to verify that the line is genuine. If I have matched with at least one other person say a great great grandparent, can I assume that the line is pure to the present day. Most of my matches (apart from immediate family) are with 3 or 4, sometimes 5 times great grandparents. The dna match in question is very much more recent, Ancestry states 1st - 2nd cousin. This person is 2 generations younger than my sister and I, so not sure which set of great grandparents or grandparents I should be looking at, or is my parents.? Can someone please give me guidance?

 

I thought I had replied in general terms but obviously not as my responding post was not allowed. It would have helped with future posts, to know where I went wrong and overstepped the mark in my generalisation. I have no copy of that post to re-examine and work it out for myself.

 

I have done this but on my offline tree but through a different connection altogether.

The families concerned lived at completely different areas of Britain. Unless one visited the are of the other, there is no apparent connection. There must have been though, so I will keep trying to find it.

Yes that is correct. I am pretty sure which side of my parents family it is through the process of elimination, which does narrow it down.
I had another good match with someone on another site but couldn't find any connection until I compared matches on Ancestry and now find that both families share a common link with each other. That is something positive and I now only have one larger mystery family to fit into my tree.

If I could determine the likely generation, it would help enormously but not being able to quote exact cMs, it is more difficult.

Thanks for your help Tim, it is appreciated.

This is the most likely answer and I have tried to pin it on one them but not been able to. My grandfather was the only male in his family but I am thinking it would be a female in my family that introduced the other family's dna. Three of us in my family have this other family's dna. I would lose a line if it was through the female line as I wouldn't be connected to her researched paternal line so I would have to swop it to the new line. If it is a half relationship, it wouldn't change anything in my direct line. Is that correct?

This is a very useful chart and I use it a lot, even encapsulated it so it stands on my desk all the time. I think I have narrowed it down now, knowing the generational gap between us. So even if you haven't given me the exact answer, it has concentrated my mind on the relationship.

Thank you for your help Peter.

 

I had a very similar situation. My AncestryDNA results came back with several matches in the 2d and 3rd cousin ranges which I could not connect to my tree. Because my mother is an only child and a very small extended family, and I was already in touch with or aware of all the branches on my father's side going back to 2d-great-grandparents, I knew there was a "non-parental event" somewhere.

I went through all my matches with trees, and grouped them by branch as best I could. Then I went through my great-grandparents one by one, and checking that there was a group connected to them. Two great-grandparents did not have matches. One was my Welsh great-grandmother; but the surprise matches all had several generations of Mid-Atlantic US ancestry, and often German or Swedish, but no Welsh. The second great-grandparent without matches came from a very extensive Irish immigrant family, although he himself was an only child. His father was one of 8 children, and he had at least 15 first cousins, and the probabilities favored finding matches. In addition, he had abandoned my great-grandmother and their children a year or two after my grandmother was born.

The next step was looking deeper into the trees of the matches. (and 2 of them contacted me, because I was a surprise close relative who did not appear on their well-researched trees). Very quickly I identified a key common surname and two generations of common individuals. Looking into this family, I found that they resided in the same area where my grandmother was born. Further research has revealed that several of the men in the family worked for the railroad, as did my great-grandfather.

It is clear that great-grandmother had an affair with a member of this family, potential a coworker of her husband, and my grandmother was the result. The story of him abandoning his family suddenly, and of his father and other relatives totally ignoring my great-grandmother after he died in an accident 4 years later, now makes a lot more sense.

Since then, I have looked further into this family. I have identified the most likely candidate: 1 year older than my great-grandmother; unmarried at the time, living nearby, and he moved away less than 2 years after my grandmother was born, then joined the Army. He did have one daughter (who would be 99 if she is still alive) -- and I am hoping there may be a descendant for a DNA test to conclusively prove my hypothesis.

 

Hi Jim,

Congratulations on getting as far as you have with identifying your NPE. At least you now know where to concentrate your efforts.
I know my paternal great grandmother was illegitimate and the closest match I have is the generation of my grandchildren, so a difference of 6 generations so is it possible that I have such a high cM count that normally would be equivalent to a 1st cousin, 1st cousin once removed or great aunt with my match. This is a significant line in my family with the most matches, of the top 8, 6 are with this family and I have identified at least another 12 positive matches to the other person but still cannot find a common link with me in any of them.

I have 22 matches with others which include just my sister and I and of those our nephew shares at least 5. None of them have trees for me to research which is frustrating. Considering I only have 165 4th cousins or closer, my sister has 276 and our nephew has 309 (he has 50% different ancestors of course) I feel a bit cheated. Might do another test when feeling a bit flush financially.

I am pretty sure it is on my father's side which is something but only having 1 first cousin on that side stops much progress and unfortuntately, they have refused to do a test after saying they would. Very disappointing.

Glad to hear you are getting somewhere with you searach and I wish you every success.