Who Ya Gonna Call? (hint: NOT Ghostbusters!)

A Segment-ology TIDBIT

The Visual Phasing process looks at full chromosomes of three siblings to determine grandparent crossover points. The Leeds Method uses Matches over 90cM to group by grandparents. Great grandparents rely on 2nd cousins (2C) Matches which average 229cM. Even out to 4xG grandparents, we rely on 5Cs at an average of 25cM. What if your genealogy question or interest is more distant?  

I recently broke through a 48 year brick wall. My known ancestor was Wilson BROWN c1751-1793 who died without a Will or any other document listing his wife or children. I’ve always known his name, because the marriage license of Keziah BROWN to Elliott BAKER in 1801 listed her father as Wilson BROWN, decd – but little else, except a probable brother Isham BROWN. Finally, the 1776 Will of James BROWN came to light – it listed 16 children including Wilson and Isham. With literally no Trees with Wilson BROWN, we have to find Match cousins from James BROWN – who would be my 6Cs.

Who Ya Gonna Call?


The average for a 6C relationship is 18cM – and over 70% of the segments are under 20cM. We have to find and use and group these under-20cM Matches in order to build a case for a 6C relationship. Boy, did I pick the wrong surname to test this out – BROWN. So I’m searching my maternal Matches with a BROWN surname below 20cM – there are many.  I’m now down to 11cM, and the “hits” in VA, NC, SC, TN, KY area are showing up. Some appear to be single “hits” in otherwise large BROWN families (not helpful);  but some are starting to group on particular lines (promising). I think by the time I get down to 8cM Matches, I will have a number of strong candidate BROWN families, with a number of potential cousins on each line. I’m letting these small segment Matches tell me lines I’m related to.

Now, I recognize that some of these small segments may be false. At the 7cM level, we expect about half to be false. But the flip side is  half will be true (Identical By Descent). When I see what appears to be a single line of descent from a BROWN ancestor in the 1700s, I can well accept that it may be a false segment. On the other hand, if a number of Matches all descend from several children of the same BROWN patriarch, I’m more inclined to think that consensus indicates true, matching, segments. Even if we insist that half of these shared segments are false, we still have a lot of them which are true and all pointing to the same family.

In my case I’m sure my BROWN line is BROWN Y-DNA Group 40 – so a link to known Group 40 lines is another reinforcing piece of evidence. Also, from my Walk The Clusters Back process, I’ve identified almost all of my greater-than-20cM Matches to a Cluster and many of those to a Triangulated Group (TG) segment. Many of the under-20cM Matches have over-20cM Shared Matches (SMs). Sometimes there is a clear SM consensus (to a TG), and sometimes the SMs don’t have a clear consensus. When there is a clear SM consensus on a suspected “BROWN” TG, more often than not, I can build a Match’s BROWN ancestor back to the patriarch of a consensus group. This further reinforces these family groups.

BOTTOM LINE – If you are looking for cousins at the 6C or 7C or 8C level, you have to rely on Small Segments! And, IMO, when you factor in that they form a solid consensus group in one family, a high percentage of them will be true segments.

[22BP] Segment-ology: Who Ya Gonna Call? TIDBIT by Jim Bartlett 20230428

13 thoughts on “Who Ya Gonna Call? (hint: NOT Ghostbusters!)

  1. So happy to read this. My Gedmatch Ancestor Project is a single surname group of people descending from a Jamestown colonist (Partin arr 1609). Very few records. Very few children for first 60 years—then the explosion of kids and mobility. You’re the first support I’ve seen in 10y for what we’ve accomplished to help people find their cousin groups. We gather around a Facebook campfire to show and analyze the Ancestor Project results of new cousins as they join and it’s how I found my 4ggf and 5Cs. Sure, some of those pretty strands of color are just from the tree of humanity, but they give us hope after decades of carving granite with a toothpick, and a motivator for me to tackle learning to read Y results (an honestly terrifying experience). Every comment here, we’ve experienced— and pooh poohing of segments below 7. I was even advised to complain to Gedmatch that Ancestor Projects are a ruse and should be shut down. But strands of wee segments are life rafts to people coming ashore into our search group after years of flailing around in bad trees and no records. And they motivate members like me to pay for a Y test. Thank you so much for this article.
    Donna Parten


    • Donna, Thanks for your feedback – glad the segments are working for you. The farther back we go, the more we have to rely on smaller and smaller segments. Be careful, though, the smaller the segment, the more likely it is to be false. Therefor the need for many such Match segments that are spread out over the family children… Jim


    • Lou, Good to see you at my blog. You have been a good partner in trying to sort out the Mayflower BARTLETTs. Our Y-DNA project is over 20 years old now, and it’s helped a lot of folks. About 10 years ago, I shifted my emphasis to atDNA (while still keeping an eye on the Y). It’s been a real learning curve, and we’ve all learned from each other – what a ride. My dad was Navy and we moved around a lot, and somehow, I never had a biology course. So, a few years ago I took a course – The Secret of Life from MITx. It’s a semester long for Non-biologists: 10 min videos (many I watched several times) – I could watch at my own time and pace – and best of all it was taught by Prof. Eric Lander (was Director of Broad Institute) AND it’s free! One night my wife called out: Jim it’s 3am – what are you doing? my reply: I’m in the lab folding proteins;>j MITx is a great program, and I now contribute to them every year – their free courses are available to anyone in the world. Cheers to you! Jim


  2. Hello again Jim
    In thinking a bit more about your new post, I have been thinking about how I might apply this strategy to myself. I understand the way you apply the percentage of
    expected false hits at the lower end of the CM range. But I’m curious how you factor in the problem of Ancestry matches whose trees may reflect more wishful thinking than reality in claiming descent from particular people. In other words, if you’re clustering matches, don’t you inevitably get some distortion from the hundreds of
    matches that have created their trees by “cutting and pasting” from someone else’s?
    Do you take those matches at face value or apply some rule of thumb that corrects for this distortion?
    Tom Walker


    • A great question, Tom! Copying is great when it’s right, bad when it propogates false relationships. I am always mindful of this conundrum, and have several “tests” I use:
      1. Consistency is often good – everyone *should* have the same result; inconsistency is a Red Flag – it usually means folks are grasping at different straws (sometimes “preferred” straws).
      2. Other obvious Red Flags – parents born/lived/died in New England – child is born in KY; parent too young/old for children; spotty list of children or list of children is way too long (usually a collection of everyone in a geographic area); weird migration (normal would be steady west and/or south); after 48 years as a genealogist, I can usually spot these issues
      3. I want to see some pertinant records! for 1810 on = census records (that match the Ancestors dates); 1782-1850 Tax List (I use these all the time in VA and a few other states). Other records that should be available for the time. If they are not in the Trees, I’ll search for them.
      4. Conform to research I’ve already done (I often find lines that tie into what I’ve already researched)
      5. If I’m just trying to find some possible leads that might build a family, I’m a little less particular – when I get a line that I want to add to my Tree, I’m much more particular.
      Can I claim 100% accuracy? NO! I often think of my family moving from Fauquier Co, VA in 1785 to the frontier of Harrison Co, (W)VA – what if a husband and/or wife died along the way? The rest of the family takes in the kids and raises them as their own! Who would ever know? These days, with a lot of DNA analysis, we might be able to figure it out. But what’s the loss if we don’t…
      I do take a Match’s parents and grandparents at face value – usually, if something doesn’t jump out.
      This is a particularly revalent issue with my current BROWN project. My Ancestor, Wilson BROWN c1751-1792 died suddenly, without Will or any other documentation of his wife or children – he should have had about 10 childen [burned county in VA]. We know two daughters through later marriage records; but no sons. As a result, folks who actually *do* descend from Wilson, have *chosen* other lines to tie into – one particularly popular line includes a Native American mother… It’s going to be very difficult to tear the hundreds of lines away from that, no matter what DNA evidence I can find (vs their NO records, but happiness with NA Ancestry).
      Bottom line to your point – I like the motto: Semper Vigilans – Always Vigilant
      Hope this helps. Jim


      • Or I guess put another way–“if it looks right—there’s a good chance it is.”
        Thanks for offering this. I’m having your tests put on a card and laminated 🙂

        Liked by 1 person

  3. I have been using my small segment matches to verify my genealogy research. Especially on my RUSH line thru my grandmother. I am able to find the connection to almost all the Rush dna matches that I have identified on her lines. I just wish I had my father’s dna. I had sent him two dna tests and his wife threw them away before he passed. I did not find out until it was too late. She thought they were junk. I use my uncle’s dna instead. Your research makes me feel better in using my small segments. I am at 6 and 7 generations.


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