Endogamy – Get the Facts!

Endogamy is sort of like a scare word for genetic genealogy. It raises a specter of something terrible that will cloud your Ancestry or your DNA. We often see Cluster diagrams with few, big blobs of color that are not very helpful. Oh, woe is me, I have endogamy…

I say: just the facts, Ma’am…  [which Joe Friday never really said]

Endogamy (and/or Pedigree Collapse) affects each person differently, but in a very specific way, in each case. Our DNA is fixed at conception – each of us has a very precise crossover points in our DNA, separating contributions from various Ancestors. We have a very specific set of DNA segments from our Ancestors. Any endogamy has already had its effect on our DNA, if any. Let’s just find out – let’s find out the facts!

1. Upload to GEDmatch.

2. Click on the free program: Are your parents related?

3. Read the intro paragraph

4. Enter you Kit#

5. Submit

6. View the results – green or red (match or no match)

Did GEDmatch find any substantial (over 7cM) green segments, in your DNA?

NO? Then, even if you had some endogamy or pedigree collapse in you Ancestry, you did not get any identical DNA segments from your parents. This means there is no effect when comparing with your Matches – every shared DNA segment with a Match will be from your father’s DNA or your mother’s DNA – no confusion!

YES? Then you do have some effect of endogamy or pedigree collapse in your DNA. BUT, it is confined specifically to the green segments. Write those segments down! Remember those segments! Put those segments into your master segment spreadsheet (two copies: one for each chromosome)! In DNA Painter: add those segments (one on each side) to highlight these areas.

All the rest of your DNA is free from the effects of endogamy or pedigree collapse. All other shared DNA segments with a Match will be from your father’s DNA or your mother’s DNA – no confusion!

Get the facts for your DNA! Free up as much of your DNA as you can.

IMPORTANT EPILOGUE – This blog post addressed the genetic, or DNA, part of endogamy. TGs are more definitive than Clusters, for example. But, it did not necessarily lighten the load on the genealogy side of our hobby. The issues of which Ancestor to link to which DNA segment (TG) remain.

[16F] Segment-ology: Endogamy – Get the Facts! by Jim Bartlett 20220425 EPILOGUE added 20220426

18 thoughts on “Endogamy – Get the Facts!

  1. Which DNA test would I need to purchase for a person to find out if that said person was born from incest between a father and a daughter? This person is elderly and not in great best health and has had strokes and numerous other problems their entire life but they want to know if the family rumors and talking was true or not? But this person and I both believe it’s very much true. She is my mom’s full sibling and is the only one living who would have been a child born from the aforementioned situation because my mom passed in 2004 and there were no more siblings or aunts uncles or grandparents left living that would be upset over the results. My aunt is the only one that I know that should be able to reveal the truth 100% no matter what they revealed. Because meant also wants to know if it’s true. And other than her it’s just me and 2 brothers left besides a few distant cousins. My granny’s siblings and their descendants? What test would tell me this information if I put the work in behind it? But I’m not rich because I still live in Eastern Kentucky. It’s a joke people don’t get upset because I love my hometown and my family and I’m proud of where I’m from, always!!!!! Which test is affordable but will help me find info I’m looking for?


    • The DNA process usually involves comparing DNA between two people. However a single test will probably indicate a father/daughter situation, because much of the DNA would be duplicated. You would need to be able to examine the data. You could test at any of the companies (Ancestry, FamilyTreeDNA, MyHertage, or 23andMe), and then upload the raw data file to GEDmatch (free) where there is a utility that compares the two halves of each persons DNA to see if there is overlap between the parents. Most people don’t have any (or much) overlap, but father/daughter parents would.
      Cost – most of the tests are around $70 to $100 normally, but they all have regular sales – sometimes down to about $50. That is a tremendous bargin when you consider that they evaluate about 600,000 specific sites on the DNA, provide a report of the results, give you a password protected website, and list everyone in their database who matches the tester.
      There is a good comparison chart of the different companies at: https://isogg.org/wiki/Autosomal_DNA_testing_comparison_chart
      These DNA tests will typically list tens of thousands of living people who are related by DNA – you may want to set up a new email address and use initials for the name.
      Good luck on your quest. Jim


  2. My parents have no ancestry in common. But some of my matches’ parents do. Usually it’s only in two adjoining lines way back, so that just adds in enough cM to make the match noticeable. But some colonial US matches have up to 5 instances of the same couple all across their tree. That’s fine too, we probably have a common ancestor back around 1600, so I’m never going to work that out and can just put it aside.
    But the killers for me are what I call “braided” matches – where a match contains several of my ancestors whose lines in their tree intermarried in a different way from my own. Fortunately these lines were also keen on family reunions and books of descendants, and with their help I can usually work out what is going on and which segment came from where. When there is no family book it becomes really hard.
    The morass for me is the parish of St Just in Penwith, Cornwall. I have sooooo many connections with DNA matches from one line or other going back to 1660. Some I have not sorted out are either before then or have just had family in the area long enough to share genes with lots of other families living there. They often don’t make it any easier by marrying people from there when they move away elsewhere, even overseas. That “locational endogamy” is a major pain for me.
    I know there is a linkage, but the common DNA segment(s) are so far no help in working out the genealogical lines. Especially when there are a few patronymic surnames shared by many and a few first names likewise.
    For anyone else in this situation, I can recommend putting together a tree of descendants from a couple way back when the records exist. It has solved heaps. Including discovering a friend (and separately, her husband) are also distant descendants of this couple.
    But, for me, there is still a lot to go.

    Liked by 1 person

      • Just beginning to have the segments to do that here and there.
        Unfortunately most DNA cousins have tested only in a segment-free zone – you know the one.
        I have managed to encourage a few to copy over to a chromosome browser site.
        Unfortunately there are many ignorant celebrities on social media going on about DNA privacy that many have been scared.

        Liked by 1 person

  3. Jim, my parents aren’t related but my paternal grandparents are 4th cousins. The family was in an isolated area of SE Nova Scotia from the 1760’s into the 20th century. While I haven’t found any 1st cousin marriages I have found just about every other combination. This didn’t bother me until I started with DNA and using DNA Painter where I was trying to map segments to CA’s. Then I started seeing relatives on my grandmother’s side (whom I had painted shades of red) showing up as exact matches for segments from relatives on my grandfather’s side (who were shades of blue). This led me to believe that what I really had was a common ancestor but one, or both, of the mapped relatives had another path which I hadn’t yet discovered. Does this make any sense?


    • Herb, Yes. I have a 3rd cousin on my mother’s mother’s side who shares 6 segments with me. It turns out I cannot say that like this: I have a 3rd cousin who shares 6 segments with me on my mother’s mother’s side. The sentences look about the same, but in fact, this 3C is also related to me, differently as a 5C, on my mother’s father’s side. My mother’s mother’s side is from immigrants in 1860s and I get very few Matches on that 1/4 of my Ancestry. But one of the Triangulated Groups the 3C was in had a LOT of Matches – that was the clue that caused me to reseach his line further and determine we were also related a different way. Jim


  4. Excellent point Jim. On the various FB sites I am continually dismayed by all the advice that essentially says any sign of endogamy is a dead end for genetic research. This is extremely discouraging. Yes, depending on the type, extent and timing of any real endogamy it is often harder, but frequently very possible to proceed with some adjustments.


  5. Jim: My Mom, now deceased, had a kit at Ancestry DNA. I am admin for her kit. After her death, a new match popped up (“John”) that looked like a male half-sib. His Y-DNA at FtDNA had 9 out of 20 hits with the same surname as Mom’s father. Subsequently, another match popped up (“Mary”), an adoptee, for my Mom that looked like another (female) half-sib. We suspect Mom, John and Mary were sired by Mom’s father. All three Ancestry datasets are moved to FamilyTree DNA so we can look at segments. Would triangulation be useful here? How do you suggest that we proceed in trying to prove/disprove a common father for these three individuals?


    • Yankee – Segment Triangulation is one good tool – but it’s the long way around to find a bio-father or grandfather. Much easier is to list the top Matches at Ancestry and look at the top Shared Matches to put them into groups. This can be done in an hour or so. Then in each group study the available Trees to find Common Ancestors in each group. Then work the descendants down from each generation. You’re looking for a descendant of one group who married the descendant of another group – that’s a BINGO: probably ancestors of your Mom. All the closest Matches of you Mom will be close cousins, somewhere close on her Tree. I’ve done this a number of times in one afternoon – it helps with two people – one reads the Ancestors in the Trees, the other one scribbles on a note pad or types – a shared libation also helps;>j I think there is a blog post: Let Your Matches Tell You Your Ancestors (I’m gardening right now; I can send a link later) Jim


    • You can do the same for each of the three – together or independently (and then compare notes). What a hoot if you all three came up with the same result – triple BINGO and bottoms up!


  6. Jim: The rest of your DNA is not necessarily free of the effects of endogamy. 100% AJ, and only 1 segment of 11 cM matches on both parents. However, there’s a match with a 2nd cousin who is related only on father’s father’s side as far as we know, but the segment shows up among other segments that definitely come from father’s mother’s side.


  7. Fantastically stated Jim. These same thoughts regarding my own pedigree collapse with my colonial ancestors have vaguely swirled around in my head for too long. Now I can really grasp the concept.

    Liked by 1 person

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