only 100 years of endogamy - chromosome mapping possible?

+6 votes
In 1766, five families, probably previously unrelated, were dropped off to settle near what became Moncton, New Brunswick.  There were a few other settlers in the area, but not many. About a hundred years later, in 1872, my great grandfather was born there, descended from four of the five families -- from two of them twice over and another one three times over.  But he left the area and married someone from a totally different background.

It has definitely had an impact on my DNA shared matches, since i have SO MANY and a large percentage of them are related to me 5 times over.  And usually they show up as 4th to 6th cousins but are actually 7th to 9th cousins.  

At first i thought that chromosome mapping would not be possible for that section of my tree.  But then i was remembering that i have no ancestry from one of the five families.  That narrows things down a bit...And there are other cousins who have no ancestry from a different one of the five families.  And there are cousins whose ancestors left the area sooner than mine, and thus are descended from only one or two of the five families. And i have found cousins from other family members who stayed behind in the States.  I started to think that it might just be possible.   It might be a very big puzzle, but it might be possible, kind of by going in reverse, not who this DNA could have come from, but who it could not have come from.

Am i crazy?  or am i on to something? or is all this premature until more people test?  Or has anyone developed any tools?

The five couples who got dropped off in 1766 are all on WikiTree: and and and and and
WikiTree profile: Heinrich Stieff
in The Tree House by Shirlea Smith G2G6 Pilot (223k points)
Process of elimination!  I'm no expert, but I have a similar 'family vine' in my genealogy, and I'm interested in learning how you make out.
I guess my first step will have to be making sure my DNA cousins have their whole tree all the way back to those 5 families and beyond, since a blank spot on the family tree that is actuality filled by one of those 5 families would invalidate my process...Yay for WikiTree, making it easier to have them all in one place!

1 Answer

+5 votes
Best answer
I would basically follow the same process I do for anyone else.  The generations thing is a guideline and not carved in granite so you adjust as more info becomes available.
by Laura Bozzay G2G6 Pilot (711k points)
selected by Shirlea Smith
So in DNA Painter, instead of making groups that seem to come from the same ancestor, i would collect the segments into groupings with headings like "all 5 except Steeves", "all 5 except Somers" etc and then keep narrowing it down as i find cousins that had that same segment but no ancestry from a specific one of the 'founding families'?
Yes you can do it by either inclusion (where someone shares say X chromosome) or exclusion where they do not share overlapping DNA on any chromosomes.  

To match you have to have a minimum of 7cm and 700 SNP for a real match.  With Endogamy you may (and are likely) to have some higher readings than normal so I would look at what the total cms indicate but also walk that back another one to two generations t see if there is a fit.

If you use GedMatch I would for sure run the People who Match 1 or 2 kits and run the kits with the highest  number of cms to see who those 2 people are all related to.  That should help to see who is excluded.  

I would also make sure to check the X (23rd) chromosome to see where you have matches as those can only come from a woman.  So if a male has an X match you know that is coming from his mother's line.  If a female does it is a bit murkier in that it can be her mother's side or her father's mother's side.  Since there can be no X transfer from father to son it helps you exclude branches.
I have a few segments that are shared by nearly a dozen cousins! that would be lovely for triangulations - except there are too many candidates for the role of MRCA couple.  Not all of my cousins have complete trees, so i guess i would have to start there and help fill in their other branches, since they, like me, are descended from nearly all the 5 founding families.  But i am very interested in your suggestion about running the 'People who match one or both of 2 kits' report at GEDmatch.  I think we will all match.  I didn't quite understand your suggestion of what to do with the report when i have it.
After you select the two GedMatch Ids you want to run for (I would assume yours and one you have a high degree of cms with) you are taken to a screen where it lists all of the people the two of you have in common.

You can select up to 14 names off that list then click on submit it the upper left hand corner of the list.  This will take you to a new screen.  Select the 3D version and you will get some charts one of which isolates any X matches.   You will also get a list by chromosome and SNP range of where you and those you selected share data on chromosomes.  You are looking for overlapping SNP ranges of at least 700
Thank so you much for nice clear instructions on how to identify new matches, but what i have is a pile of very good matches for which i have multiple MRCAs.  No doubt the cousins and I are all descended from all of the MRCAs - there is no reason to doubt these trees--this family connection has been well documented, although there are possibly additional, as yet undocumented, lines of descent from the same set of ancestors.  What i am trying to do is pin down which chromosome segments came from which particular ancestors.

I do understand how to do this if there are only two possible candidate couples - Roberta Estes' blog has been very helpful. But five and the Loyalists who followed them?  I'm looking for tips, pointers, or even advice that maybe it is premature to attempt this yet.  If i was looking at deep endogamy for centuries, i would not be trying, but maybe someone has been able to work through a similar shorter-term endogamy?
Shirlea that is where mapping the branches I talked about comes into play.

After you run the People who match 1 or 2 kits you see everyone who matches those 2 people in Gedmatch down to the chromosome and SNP level.  So what I do is also run the one to many report and copy it to excel.

Then I create a column and list which branches hit which people.  

By mapping it this way you see patterns forming.   You may have one person who matches all 5 families but another that only matches 1 or 2 or 3 or 4... You are looking for those points of both commonality and voids.   I hope that is making sense.   You may find that 3 families consistently match on chromosome 3 while others match on 3 and 10 for example.  

I am not saying this is fool proof but by plotting the results you do see patterns forming.
Thanks so much, Laura!  I've been assembling data and getting ready to try this!

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