Is there any significance to 20 people all showing triangulations on the same chromosome as my mother?

+7 votes
261 views
I went through some more of my mothers DNA matches this weekend and I found one man whose 3 daughters plus himself have all tested. They all have between 25 and 50 cM of shared DNA with my mother, all on the same chromosome and NONE of these people are in my own DNA matches list. The relationships is estimated to be 3rd cousins, 3C1R or 3C2R.

Using my mother and this same father I found almost 20 other people who all have the same segment on the same chromosome triangulated with my mother, and again, none of these names are on my DNA matches list.

Is this significant or not?
WikiTree profile: Robynne Lozier
in Genealogy Help by Robynne Lozier G2G6 Pilot (929k points)
You didn't mention which chromosome so you might want to check if it is one of the 'pile up' chromosomes. Article here: https://isogg.org/wiki/Identical_by_descent#Excess_IBD_sharing
Sorry. The triangulations are all on Chromosome 5

3 Answers

+4 votes
Robynne,

I do not see this as unusual.  I have many cases where I have a solid DNA match with a known cousin (3rd or higher) but my full siblings do not.  In addition they have matches with known cousins (3rd or higher) and I do not.

My suggestion is to work out the relationship and document with a solid paper trail - most likely I think you will find a cousin and be able to fill in one more branch of your tree.
by Philip Smith G2G6 Pilot (287k points)
Thanks Philip. Knowing this is not terribly unusual is helpful.

How to work out the paper trail is going to be hard. Most of these people do not have good trees and if they are not into genealogy, I have no way to even start thinking about where we might be connected.
Robynne,

I am amazed and often frustrated by how many people add DNA tests at various sites but when there is a match and they get an e-mail they do not reply.  Even so - I suggest you send a note to each to the people.  Perhaps one will reply with a clue.

If there is just a bit of a tree you can sometimes work it out - but it is a lot of work.
Actually if you watch all the DNA test videos on youtube - most of these people who do these tests, are doing them JUST for their ethnicity estimates and NOT for the genealogy!!

That is what is so frustrating about this.

Don't look a gift horse in the mouth!

At worst, these matches provide no information, which leaves you in the same place you'd be if they hadn't tested at all.

But sometimes the actually give a little info (despite themselves!), and that's enough to get something useful out of their poor choice as a consumer (buying a product for the useless, almost fraudulent part, instead of the actually useful part) smiley!

+2 votes
Indeed - it's not unusual at all. It's actually a blessing to have these matches to your mom.

On every given segment your mom has, one "side" of it is from her mother, and the other is from her father. So suppose, for example, you got the side of that segment of your mom's DNA that has your maternal grandpa's DNA, but these are your relatives on your maternal grandma's side - you're not going to match them on that segment, and therefore possibly not at all!

So it certainly IS significant - it tells you that your own segment there (the side you get from your mom) is for the opposite side of your mom's family from these other people. That will be more useful once you find out which side of your mom's family they're on.

Conversely, if you find out which side of your mom's family YOUR segment there matches, then that tells you that those guys are on the OTHER side. So you would only have to investigate the possibilities on half your mom's tree, instead of all her tree.

In summary, I concur. There's not only nothing wrong, but it's common - and useful information - once you get the hang of how this works. It can get a little tricky!
by Frank Stanley G2G6 Mach 6 (67.0k points)
+1 vote
Hello,  Yes I think that is a legit DNA connection.  

I just found a similar case in my own families DNA.  I was checking out my nephews matches and saw one with a surname that was my paternal grandmothers mothers surname from Netherlands.  

I was not sure of the parents of my immigrant ancestor on that line who came over in the 1880s or so from Netherlands.  I had found some records I thought were a match but no conclusive records to match the two.  

However this DNA match had over 1,100 people in their tree at My Heritage and so I was able to find that we have a common ancestor on that family line going back a few generations up from my immigrant ancestor to 1700s Netherlands.  So this confirmed the records that I had found, it was the correct family!

It was like a 20cm au DNA match.  I checked my own DNA match list but I did not have a match.  So it ends up my father, sister and nephew all have that same segment of Dutch DNA but I did not get it.  I think they all had a similar size match, about 20cm +/-3.  Oh the DNA match was with both a mother and daughter.  So there are 3 of us on our side and 2 on their side who match.  Pretty neat!
by Erik Granstrom G2G6 Mach 2 (29.7k points)

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