Trees that don't match

[sunflower]

Is it too simple to assume that a match sharing 2 x great grandparents, (3rd cousins) the same name(s) will appear in both matches' trees. The connection being through their offsping and descendants.

 

[peter]

If I've understood you question correctly, all you would know is that they share the same 2G grandparents.

 

[sunflower]

I realise that but having researched both trees back to 3 x great grandparents, there is no common name, so just wondered if I was taking too simple approach to sorting out the connection. I can tie in many other matches with the connection to this other tree but not to mine. I am pretty sure I have the correct side of the family but as that is a side I did not know existed until recently it is proving to be quite difficult and I need to do more research.

 

[Pauline]

I may be missing something here, but how do you know they share 2x great grandparents if you haven’t identified them in both trees?

 

[sunflower]

Both Ancestry and My Heritage have indicated that is the common ancestor. Should I not be guided by their assumption?

 

[Pauline]

Should I not be guided by their assumption?

Not as a certainty, it’s only meant as a rough guide based on averages. So the average amount of DNA you might share with a third cousin is around 73 cM, but you may not share any DNA at all or you may share as much as 235 cM. Ancestry give a range of possible relationships if you click on that given for each match in the match list, but there may be other possible relationships too.

There is a useful chart in Peter’s masterclass showing the possible DNA ranges for different relationships.

 

[sunflower]

I have that chart encapsulated against wear and tear and it is used constantly. We share 96 cMs so 3rd cousins seems to be the most likely although I do agree, there are other options. Unfortunately, the other person has taken their dna results down from Ancestry so I cannot check there any more but it is still live on MH although never updated. MH gives the match 49.1 % it being 3rd cousin the next ones are in single figures so I guess that is pretty conclusive. I have access to my sisters and nephew, son of my brother, results and we all match with this person but my match is higher.
It is a shame that the other person took down their tree and results as I now have access to the genetic paternal side of my family so I could have checked if they matched as well. Unfortunately, they are not on MH. I think they have dropped any contact with me as their family cannot accept the reuslts in conjunction with my family. Nothing like the happy reunions you get on the Lost Family programme.

I am in the process of checking all the lateral lines now so may come up with something to tie it all in. On the other hand, I suppose, I could be barking up the wrong tree completely.

 

[Pauline]

The difficulty always is that the amount of DNA shared can be so unpredictable. For example, I have a documented 4th cousin once removed with whom I share twice as much DNA as I share with a documented 3rd cousin in the same line. (That is, all 3 of us share two common ancestors.) There are also numerous matches with whom my sister and I share a vastly different amounts of DNA. And I have more than a few matches where the documented relationship falls into the less than 10% chance category.

Of course (stating the obvious) if there is 49.1% chance that this match is your 3rd cousin, there is a 50.9% chance that they are not! What relationship is predicted to other members of your family?

 

[sunflower]

My two sisters do not have as much of match as I do but the one with 58.7 cM has 29.3 cMs as a 3rd cousin and 26.3 as a 4th cousin and various other smaller amounts. The other one has only 27 cMs so more likely to be a 5th cousin with 24% or a 4th cousin with 22.8% possibility. I guess that matches your last reply, so I need to cast the net a bit further back.

So in answer to my original question, yes, it is too simple an assumption. On my MH matches, this person is my first non immediate family match.

Thank you for highlighting the reason why I cannot match any names in my tree with the other person. Yet!

 

[peter]

The difficulty always is that the amount of DNA shared can be so unpredictable.

It is, once you get past 1st cousins - one of my 3rd cousins shares only 10cM with me, less than one of my 6th cousins, and little more than my 8th cousins. I never take any notice of the predicted relationships, which are primarily a way of sorting matches into some sort of order.

 

[Sue_3]

I have a 4th cousin that I only share 6 cM with. We were connected before DNA testing as we are both descended from a family with a surname that is unusual in the locality and have been collaborating for years.

 

[sunflower]

Thank you everyone for your comments which I have taken on board and learnt from.

 

[peter]

I have a 4th cousin that I only share 6 cM with. We were connected before DNA testing as we are both descended from a family with a surname that is unusual in the locality and have been collaborating for years.

There are two people in my tree who are 2nd cousins once removed but according to Ancestry don't share any DNA (and this was in the days when the threshold was 6cM rather than 8cM).

 

[sunflower]

I guess that is what makes us all so individual.

 

[peter]

I guess that is what makes us all so individual.

DNA is essentially random - although we get all of our DNA from our ancestors, once you get beyond your parents how much you have inherited from each ancestor is fairly random.

Furthermore, even if you and a cousin have inherited a lot of DNA from the same ancestor there might not be any overlap. Only for very, very close relationships can you deduce anything from the amount of DNA shared. So it makes sense to ignore any suggestions as to how you are related to your genetic cousins.

 

[Sue_3]

DNA is essentially random - although we get all of our DNA from our ancestors, once you get beyond your parents how much you have inherited from each ancestor is fairly random.

Furthermore, even if you and a cousin have inherited a lot of DNA from the same ancestor there might not be any overlap. Only for very, very close relationships can you deduce anything from the amount of DNA shared. So it makes sense to ignore any suggestions as to how you are related to your genetic cousins.

Well, maybe not completely ignore, but accept that there is always a very wide range of possibilities, so don't be overly constrained by them. It's like all evidence, it points in a direction, but can be misleading. Also need to bear in mind that anyone can be mistaken as to who their biological parents, or their ancestors biological parents, were. So, if you are looking for biological certainty, you cannot fully trust anyone's tree, including your own, unless there is compelling DNA evidence to support it. However the lack of DNA evidence does not necessarily disprove a tree. We always have to weigh up all of the available evidence and determine what is most likely and, moreover, what is most important. In my book, the social family and lived experience are, or can be, just as important as where someone's DNA comes from.