BLUF (Bottom Line Up Front) – you may already know this: The average cMs of all your Matches in a Floating Branch back to the Common Ancestor (CA) is a strong clue to about your relationship (use judgment to pick the CA and cull out outliers); and the highest average among the children of that generation would often point to the child you descend from.  

This is an insight based on collected data. First, we’ll set up the situation:

A Floating Branch is a group of your Matches who all descend from a CA who is not one of your known Ancestors. Typically, a Floating Branch can contain a lot of Matches (I’ve seen 20, 50, over 100). It’s frustrating – their CA is almost certainly your CA, but the link eludes you. It’s probably one of your Brick Walls, or beyond.

Brick Walls – to me, there are at least two types of Brick Walls – Ancestors in “plain view” and Ancestors “hiding under a rock” (or abducted by aliens). The “in plain view” Brick Walls are out there, with records, but we just haven’t made the genealogy connection. But, in my opinion, most of our hard Brick Walls persist for a reason: there is little to no information about them. My favorite example is a tic mark on the 1840 census (perhaps a young man who impregnated a young woman; and went “west” in 1849 and died along the way). The parents of the tic mark are known, but no other info on the son. There are many other reasons why a person may not be in the records. If they had left records, they probably wouldn’t wind up as Brick Walls.

Think about these two concepts (Floating Branch & Brick Wall)… To my thinking, they should “link up”. But how?

Well… After we’ve done an exhaustive review of the Floating Branch (fill out the descendants of the CA; ethnicity; geography; records, etc.), we probably have at least two things we can do with the collected DNA data. One is to average the cMs of all the Matches (except obvious outliers) and use the Shared cM Project to make an educated guess at the probable relationship (and generation) of our connection to the Branch. Ask: what Brick Walls do we have at that generation? Yes, it gets harder and harder as we go back in time.

However, the gist of this post is to figure out where we tie into the Floating Branch.  It’s where the highest cMs are! Probably obvious to Segmentologists…   

Take a known Ancestor with, say, 8 children; we would usually see Matches from most of the children having one average cM amount, while the Matches descending from the child who is our Ancestor will have a higher cM average. Again, easier to detect with close relationships.  In theory, the difference is a factor of 4. If most of the Matches are 2C averaging about 229cM, we find the 1C Matches with the child who is our Ancestor to be about 866cM. See this table for different generations:  

Matches with most of the children vs Matches with just your Ancestor child:

Great grandparents                   229cM for 2C vs 866cM for 1C – pretty close to 1:4

2xG grandparents                       73cM for 3C vs 229cM for 2C – a little more that 1:2

3xG grandparents                       35cM for 4C vs 73cM for 3C – about 1:2

4xG grandparents                       25cM for 5C vs 35cM for 4C – still more, on average

5xG grandparents                       18cM for 6C vs 25cM for 5C – still more, on average

In other words, the floating branch should have an array of Match cMs just like any of your known CAs has any array of descendant cousins – roughly like the Shared cM table shows.

The point is that if you had a Floating Branch, and didn’t know where you tied in, averaging the cMs for each child at the same generational level, might provide a clue.  I have two cases where the probable link sticks out like a sore thumb; and 2 others where the averages are not as clear as I thought they should be…

I’ve had this thought before – see here; and here. The more data (Matches), the better.

I’d be grateful for feedback from anyone who works with Floating Branches and has enough data to indicate whether one path sticks out like a sore thumb… And/or if you have any thoughts, pro or con, about this kind of analysis to squeeze a little more out of a Floating Branch…

[22DM] Segment-ology: Where Is Your Ancestor in a Floating Branch? By Jim Bartlett 20260629

As I noted in my last post (Drinking Through A Fire Hose), I have over 10,000 DNA Matches with pretty solid genealogy paths back to our Common Ancestors. I’m about 1/3 of the way through entering and Tagging these Matches and their paths back to our CAs in my main Tree at Ancestor.

Let’s look at an example. My Ancestor [A0856] John HIGGINBOTHAM b 1695; married 1713 in Amherst Co, VA to Frances RILEY. I have identified 827 DNA Match/cousins who descend from them.

Note 1: most of my Matches do not have a Tree back to John – I and ThruLines determined most of the paths.

Note 2: search Public Member Trees for John [drumroll….]: 10,323 Trees! WOW! Take a guess at how many Ancestry members actually descend from John and Francis, but don’t have Trees that reach 9 generations back…  – 100 thousand? A million?

Note 3: take a guess at how many DNA test takers there are in addition to the 827 folks I have already documented back to John and Francis. I’m sure it’s a LOT!!

Suppose we were all working within one Tree…

Over the years there have been several attempts to establish one family tree: OneWorldTree (Ancestry); World Family Tree (Geni); World Connect (RootsTech); WikiTree; FamilySearch Family Tree. IMO, there are a lot of issues within these attempts, as individuals interpret records differently, or worse, enter names and relationships without any documentation, etc, etc. Many NPEs are never discovered…

Concept: suppose we started Tagging ourselves, our DNA Matches, the DNA Connections, and the DNA Common Ancestors in WikiTree or FamilySearch.

As I wrote about in “Advanced Genetic Genealogy, Techniques and Case Studies”, I had identified three separate Triangulated Groups from John HIGGINBOTHAM and Frances RILEY [my 7XG grandparents – Ahnentafel 856].  In other words there were three finite segments in my maternal DNA that were in each of my Ancestors going back to John or Frances; and a shared/overlapping  DNA segment [part of my segment] in each of my 827 Matches, and in their Ancestors in a path of descendants from John or Frances down to and including each Match. [Remember each Match overlapped some of my DNA segment in the full Triangulated Group.]

Note that, on average, each of my Matches probably also had about 3 segments that went back to John and Frances. And I am not the center of the universe – all the other DNA test takers have their own, independent, experience. Certainly, there were many other descendants of John and Frances who had different DNA segments.

So what benefits would accrue to this concept…

1. Our accumulated Tags would provide a consensus that the paths we shared back to an Ancestor, passed through true genetic genealogy paths. This would be evidence that was independent of the genealogy analysis.

2. Perhaps a TG segment was actually from a different Ancestor. In the grand scheme of DNA, there would be certain distinct DNA segments that would be passed down from each Ancestor to various living test takers. It seems to me that, in general, these would wind up in multiple descendants. Note: we know that a given DNA segment could possibly be from a range of Ancestors, but when a number of DNA test takers all have the same [overlapping] DNA segment, it must surely be from one Common Ancestor.

3. So, this concept would help weed out which DNA segments came from which Ancestors.

4. Also, we’d start to accumulate specific DNA segments that came from specific Ancestors. We’d have the accumulated data to “paint” some of the Ancestor’s DNA.

I’m looking for feedback on this post. Pros and cons… Additional ideas… Is this already being tried? Shouldn’t we Segmentologists be working on a way to share and combine our DNA data to benefit each other? I’m looking for better language to articulate the possibilities and/or drawbacks of this concept.

[22DL] Segment-ology: A Concept Project for Segmentologists; by Jim Bartlett 20260622

I have incorporated all of my AncestryDNA ThruLines and MyHeritage Theory of Family Relativity Matches into my Common Ancestor spreadsheet (see Chapter 7 of the free book, Segmentology Fundamentals, at ISOGG). Here is a tabulation of Matches with Common Ancestors (CAs) at all companies:

23andMe                 167

Ancestry           10,435

FTDNA                      239

GEDmatch              170  [I’ve not been able to find these at the other companies]

MyHeritage            261  [this includes 113 from Theory of Family Relativity]

Total                    11,272

Clearly AncestryDNA leads the pack; but note that at the other companies, all the Matches have known shared DNA segments in specific Triangulated Groups (TGs).

Here is a breakdown of Ancestry by category:

ThruLines         8,516  [includes 144 wrong but fixed;  plus 104 which are now gone]

No Tree                   175  [determined by Pro Tools]

Private Tree            27  [determined by Pro Tools]

Unlisted Tree      531  [Note the large number of Matches; not found by ThruLInes]

Found in Tree   1,186 [Just searching]

Total                    10,435

Of the above 10,435 Matches at Ancestry

• There are 1,078 (roughly 10%) that I have tagged as incorrect – and I move those out of the active part of the spreadsheet
• There are 741 Matches with known shared DNA segment in TGs [plus 328 additional Matches for whom I don’t know the CA]
• There are 6,885 from 5xG grandparents or closer (nominal 6Cs) – this reflects the power of ThruLines to find them.
• There are 2,077 Matches from 6xG grandparents; 1,232 Matches from 7xG grandparents; and 181 Matches from more distant Ancestors.

Note – some of the Matches are listed more than once when they are related to me multiple ways; some because they tested at multiple companies.

So what’s the point here?

#1 is that I’m drinking through a fire hose!  Granted that I’m retired and can spend time on genetic genealogy…

#2 is that the data is out there – or rather, the data is here, within the reach of the major DNA companies…

My morning routine includes seeing if there are any new ThruLines at Ancestry or any new Matches at GEDmatch (particularly Ancestry ones). Often I cannot get through that chore before I have to break for other responsibilities.

If I have time, my next task is working down my Ancestry Matches in my Common Ancestor spreadsheet and evaluating their shared Matches with Pro Tools. I didn’t have Pro Tools when I first developed the CA spreadsheet, so there is a lot of catching up to do.

It’s a two pronged approach – enter the Match in my Tree [tagging them: “DNA Match” AND using a special Dot in their profile when I do so] and entering their path to our CA [tagging each person: “DNA Connection”] in my Tree; and then evaluating the shared DNA Matches using Pro Tools [sorted on the Match’s relationship]. I’ve done this through my 4xG grandparents and now have 3,368 Tagged Matches. Still thousands to go, plus all of the new Matches with CAs I find with Pro Tools.  Drinking through a fire hose.

The point is that I’m building a large family of DNA-linked descendants for each Ancestor – easy to review in the CA spreadsheet and in my Tree. AND, as I find more and more Matches with segment information, the consensus builds for Chromosome Mapping info.

[22DK] Segment-ology: Drinking Through a Fire Hose; by Jim Bartlett 20260616

Free: Segmentology Fundamentals eBook available for download at ISOGG/Wiki