Shared Matches

[Tim]

I have a cousin Emma who is a cousin once removed with 125 cm accross 9 segments, my grandfather is her great grandfather. There are 2 Shared Matches: John who has 43 cm accross 3 segments (predicted 4th cousins) and Kerina 20.9 cm across 2 segments (predicted 4-6th Cousins).

If I look at John's shared matches, it says Emma and Kerina.
If I look at Emma's shared matches, it says John only.
If I look at Kerina's shared matches, it says John only.

Am I missing something? Why doesn't Emma have Kerina, and Kerina have Emma?

And presumably the connection must be in my Grandfathers ancestors somewhere.

 

[Helen7]

Am I missing something? Why doesn't Emma have Kerina, and Kerina have Emma?

It looks like Emma's match with Kerina and vice versa might fall below Ancestry's shared match threshold of 20 cM. I see Kerina is close to that threshold with her match to you, so could well be less than that with Emma.

I have a 2nd cousin (call him A) with a match to me of 169 cM across 8 segments, with whom I have 4 shared matches (B: 59 cM, C: 54 cM, D: 33 cM, E 26.5 cM). Whilst A, B, D and E all have shared matches with each other, C is the odd one out in that C only has a shared match with A and not B, D or E. I found this a bit surprising given the strength of C's match with me. I have been in contact with A and B and established our relationships (B is a 4th cousin, her great-grandfather being a 1st cousin of my and A's shared great grandfather), but establishing connections with the other 3 has proved difficult up to now - none have a tree on Ancestry, D and E haven't logged in for several months, and C though logged in today has not responded to messages.

And presumably the connection must be in my Grandfathers ancestors somewhere.

I have found that my shared matches usually indicate the common line of connection, so it looks likely to be your grandfather in this case. Have you tried contacting John and Kerina to sort it out? Hopefully you will have more success than me in the example I describe above!

 

[jorghes]

I believe that they will only show shared matches when the match is "4th cousins" or closer. Or something like that.

So my presumption would be that Kerina and Emma don't have enough shared between them to appear as Ancestry's denoted "4th cousins" and therefore won't appear on each other's shared matches.

 

[Tim]

I haven't contacted Kerina yet, but I am building her tree as we speak. I have contacted John and we share trees, but we can't find the missing link yet.

 

[Tim]

What would be useful for me here is to see which segments we match on.

 

[peter]

What would be useful for me here is to see which segments we match on.

You'll have to ask your cousins to upload their results to GEDmatch.

 

[peter]

Shared matches are dangerous for all sorts of reasons. For a start some people assume that if they have lots of matches with cousins who all match each other that the matches are going to be easier to resolve.

In practice the reverse is usually true. Where there are lots of people who share the same segment this generally indicates that the common ancestor is much further back than expected - the connection is to a population in which the DNA segment is common.

Another pitfall is triangulation. Different people mean different things by the term, but a typical interpretation is that if A, B and C all match on the same segment the matches are somehow more likely to be genuine. In fact the reverse is the case, for the reasons given above.

Frustrating as it may be that Ancestry limit the information they provide, I suspect that in the majority of cases it's for the users' own good. My own experience of wasting hundreds of hours at FTDNA and GEDmatch is testimony to this, though trying to persuade someone who is hooked on GEdmatch that they're probably wasting their time is impossible!

 

[jorghes]

What would be useful for me here is to see which segments we match on.

Or perhaps checking for further “shared matches” to attempt to narrow down the branch of the tree that you need to be searching.
Frequently I will add notes to each of the matches - occasionally it will be as detailed as “2C2R decesdended from X & Y”, other times it will be a query like for one of my grandmother’s results it just reads “Scottish side?” - referring to her father’s side of the tree as I am unsure of the exact link (and there are no surnames to search through re: Peter’s Masterclasses; or they have no tree at all and that’s what is suggested by the rest of their “shared matches” and previous notes)