Help with a 3 way DNA connection

[jillruss]

I don't possess a scientific brain so, try as I may (and I have) I can't get my head around the science of DNA other than the basics.

I wonder if anyone can give any advice or help with a quandry that myself and a lady in Australia are trying to sort out.

I'll try to keep it as short as possible:-

a) I have a 4-6th cousin match with JK - details are 26.4 cMs over 3 segments. She lives in the UK and I have pretty much established that we have a 5th gt grandfather in common.

b) I also have a 4-6 cousin match with PJ from Australia - 21 cMs over 1 segment. We have located a possible match, again with common 5th great grandfather (not the same 5th greats as in a) above but on the same side of my tree (paternal) and in similar geographical locations ).

c) There is also a 4-6 match between JK and PJ - 23.6 cMs over 1 segment. PJ and I have been trying for quite a while now to fill in as many siblings and spouses of relevant generations as we can but so far there is no sign of the connection between JK and PJ which - unless I'm much mistaken must realistically be between two of my branches. Those two branches do marry into each other on my tree but not until  a lot later: my 2xgreat grandparents.

The conundrum has added mystery in that PJ's father was adopted with origins uncertain.

I don't know if the number of segments in a match is as key as the cMs?

I know sugarfizzle and a few others are quite well versed in the science and I'm hoping you may have some pearls of wisdom to impart!

Thanks,
Jill

[diplodicus]

The only non-circumstantial way to answer your question is for each of you to upload your DNA results to something like gedmatch.com. Gedmatch is free and there are clear explanations on how to do this on the gedmatch website.

You can then examine each chromosome and see if any of your matching strands overlap and if so, by how much.

It would be interesting to run their "show results that match both samples" utility to see how the third relates to each.

I am sure there are other ways but that's how I would do it.

[hurworth]

DEFINITELY use a site with a chromosome browser. 

It's nigh impossible to analyse your matches without a chromosome browser, which Ancestry doesn't have.  As well as Gedmatch I use FamilyTreeDNA and MyHeritage.   

[jillruss]

See - this is where the science bit comes in that I wanted to avoid. 

By the way, I did already upload my DNA data to Gedmatch - and was totally underwhelmed by it. it gave me a list of matches, most of which I already knew about from Ancestry and, like Ancestry, most of which didn't have trees. I've been on Gedmatch since and looked for any new matches in shades of green but there never are any.

So, say if I did understand how to "examine each chromosome and matching strand" what would that tell me other than where the three samples match? I'm not sure it would be much help anyway. Would it enlighten me as to which generation I should be looking at?

But, thanks anyway. 

[sugarfizzle]

To add to what diplodicus and hurworth have already said.

You match with both JK and PJ. You have established this connection beyond reasonable doubt, I assume.

The fact that JK and PJ are also matched with each other does not of itself indicate that all three of you have common ancestors.

The fact that PJ's father was adopted complicates matters somewhat.

Is your connection with PJ assumed to be on his maternal or unknown paternal side? Whichever one it is, JK could match with him on the other side.

I have A in my tree, but not a direct ancestor, half sibling of one. My husband is a confirmed DNA match with someone else B, whose direct ancestor is A.

My husband and and I are not related in any way, it's just one of those coincidences in life. Assuming our daughter inherited sufficient DNA, she might share DNA with B and also matches with my side, say C who is descended from A's line.

But B and C would not be related at all.

I don't know if I have explained that very well!!

Chromosome browser definitely the way to go, if you can persuade the other two.

Regards Margaret

[diplodicus]

It's a shame you are underwhelmed as I have found Gedmatch really useful.

As I understand it, at the moment you may not yet be certain that A matches B matches C matches A.

You know. that A matches B; and also that A matches C; but you don't know for sure that B matches C unless you have asked B and C to confirm between themselves that they match each other.

Gedmatch can provide that certainty by using the 2-D chromosome browser to see the there is a statistically significant overlap somewhere along one chromosome.

Having said all that, as you travel further back, the chances of finding shared DNA diminish sharply and all the testers tell you that there is a high probability of not finding matches between common ancestors.

I have Welsh ancestors on both sides of my tree and having known shared matches from both sides has helped me identify on which other side some of my other Welsh matches are positioned. The "People who match one or both of 2 kits" function in gedmatch may prove useful?

[jillruss]

Thanks, both.

Diplodicus: yes, we DO know that B (PJ) has a match with C (JK) - this is the one we can't find. Unfortunately, C has not shown much interest in discovering the connections so its very much a two-woman project and I don't reckon much on my chances of getting JK to upload her info to gedmatch.

The matches between A (me) and both of the others are well researched and, in the case of B (PJ) involving many other matches which so far corroborate our findings.

Margaret, I'm so pleased you've replied as you always seem to be very knowledgable on the subject of DNA. We had considered that the match between PJ and JK might be a coincidence or even on PJ's maternal side (the match between myself and PJ is - we think - on the adopted father's paternal side). I thought the chances of a coincidence were very long indeed, but you've made me rethink that.

I'm still struggling with this chromosome browser. I can see, from what you've both said, that it might be possible to identify a chromosome match but does it tell you any more than that? Would it point us to put more research into a specific generation? We already know we have matches but what would the browser results add to that?

Apologies if I'm being dense - I gave up all my science subjects after GCEs!!

Jill

[sugarfizzle]

Jill, My knowledge about DNA is more practical based than science based, a lot of it goes over my head, even with reading up about it.

I know how things have worked out for me with DNA testing, which is why I very often give examples.

I am currently looking at a match who shares my paternal 7G grandparents, according to both our trees.

However, our 2 shared matches are from my maternal side, they both share my 4G maternal grandparents.

No known connection between my parents, other than by marriage.

Without all parties uploading elsewhere I am unlikely to find exactly where we match and whether the shared matches are really shared ancestors.

Regards Margaret