Could the expected cM for 18th to 22nd cousins be 7.5 or it is a false result

+7 votes
Would a match between 4 people on  Chromosome 6 at an average of 7.5 cM and 4000 SNP's  when the relationship finder here tells me they are between 18 and 22 cousins?   The Generations to MRCA est on GEDmatch is 7.4 to 7.5.
in Genealogy Help by Mel Lambert G2G6 Mach 3 (32.1k points)

3 Answers

+6 votes
I'm sure the relationship here is simply the maximum and if it's the connection finder, it includes marriages anyway.  We've only got a tiny fraction of the people in the world on the tree, so there can be any number of missing connections which will ultimately be here.  The GEDmatch figure looks about right.  You just need to check the other matches using the e-mail addresses and see if you can find the actual MRCA for the group.  I've been sorting my matches by chromosome and for chromosome 6 I have group of 6 matches near the beginning, 3 at 160 million, and 2 at about 138 million as well as 4 other singles at various points.  I need to start e-mailing people, but haven't gotten to it yet.
by Dave Dardinger G2G6 Pilot (410k points)
+7 votes
Mel, It's extremely unusual for auDNA to provide useful information further back than about 5th cousins. Are your ancestors part of an endogamous group--lots of intermarriage? I think that's the only way you might see that much DNA in common back that many generations, and even then, 18th to 22nd cousins seems too far back.
by Kay Wilson G2G6 Pilot (198k points)

:)   :)  They were from Virginia/ West Virginia  so yes there were intermarriages.  My 2nd great grandfathers were  first cousins which makes my great grandfather and mother second cousins. 

The matches I posted are all from here.and are from the Sampel / Sample / Samples line.   I started this when I found duplicates in the Sample/s line. Moses Sampel  Moses Sample and Moses Samples along with the wife, Ruth Wood Sample/s .  I was shocked when this match came about because they are from an unconnected line of Samples from NY.  Yet my Mom does not have very much DNA in line with  the other DNA matches for Moses.  



I don't understand how you could have 18th to 22nd cousins from Virginia and West Virginia. The oldest Samples profile you have on your tree is your 6th great grandfather who was born about 1664 in Ireland. If you share him with another person you would be 7th cousins, not 18th. With 6th cousins and endogamy I don't think your results look too unusual. But Peter is right--you will need three or more distant cousins all matching each other on the same segment of at least 7 cM.
The 18 to 22 cousin came from the relationship finder here.  If this is a true match somewhere our lines have merged and it is just not known yet.  Or it just may be a fluke that showed up  while I was running the Samples data.

DNA is still new to me.  Like most newbies I am reading lots, learning slowly,full of questions and making mistakes.  

I hope my questions dont drive everyone too nuts.
After I wrote you it occurred to me that you may be mis-reading the information on the 'Relationship Finder' page. Instead of looking at the 18/22 in the 'Explore more' section of the page, look at your relationship displayed at the very top of the page. It will say something more like "John and Mel are 6th cousins." Then below that it will give the relationship trail for each of you back to the first common ancestor on WikiTree for the two of you.
No I read the top  "John and Janice are 15th cousins twice removed" I have even run a family list for 9 generations on both Janice and John and there are no common surnames.  If this is a true result then we have to be missing the common link.   I am starting to think it is just a fluke .

My mom's DNA does not match many of the Samples on this site. On FamilyTree she has only 3 matches with in the 2-4 cousin range.  She was one special lady and I guess her DNA proves it
+1 vote
Beyond third cousins you need three or more distant cousins all matching each other on the same segment which measures at least 7 cM.

It is my understanding that some segments can get inverted.  Unless a cousin also inherited part of that same inversion, you will not (or rarely?) find (7+ cM) matching  on that portion of your chromosome.  Sometimes very distant cousins who share the same inversion will match on a relatively large segment given their distant relationship.  

Is there a geneticist in the house who can confirm or correct my understanding?  Thanks.
by Peter Roberts G2G6 Pilot (607k points)
edited by Peter Roberts

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