About Jim Bartlett

I've been a genealogist since 1974; and started my first Y-DNA surname project in 2002. Autosomal DNA is a powerful tool, and I encourage all genealogists to take a DNA test.

Percent of Shared Cousins Indicates Relationship


Subtitle: Teamwork in Practice

In my last blogpost about my ancestor Wilson BROWN, I hinted at a large group of Shared Matches to a Thomas BROWN b 1773 (m Nancy LITTON). Over 2,000 people have this Thomas in their Trees at Ancestry. After some collaboration, I was given access to the DNA kit for the person named MATCH in the diagram below [credit to Allen Brown]. I wanted to look at the ThruLines Matches for MATCH. Well… it turns out MATCH has 756 ThruLines Matches from Thomas BROWN b 1773, spread over 7 different children – just WOW! I looked at 276 of them, spread over 5 different children (not including MATCH’s direct ancestor). I clicked on each Match name to see if I was also a match to that person. Drumroll…. 28 of them were also DNA Matches to ME. So, using this information, how is Thomas 1773 related to ME?

Diagram of descent from James 1705 to ME and descent from Thomas 1773 to MATCH:

Remember the rough guidelines that true 2nd cousins (2C) will match 100% of the time; true 3C will match 90% of the time; true 4C 50%; true 5C 10%; and true 6C 2%? My little exercise resulted in ME matching 28 of 278 given cousins identified by ThruLines for MATCH. This is right in line with our expectation for a 5C!  In the diagram above, Thomas would most likely be the son of Wilson, rather than a nephew (which would result in a 6C relationship between ME and MATCH). Note: we had already determined that the James BROWN 1705 line and the Thomas BROWN 1773 lines were both in Group 40 of the BROWN Y-DNA Project.

Maybe this is a fluke. I’d like to find another Match descendant of Thomas BROWN and see if I have the same ballpark results. Also, I’m still reviewing all of my AncestryDNA Matches with a BROWN Ancestor to see if there is another firm group (or Cluster) of BROWNs, so I can see if they also might descend from Wilson BROWN. Spoiler alert: I do have a very large (100 Match) Cluster that I have linked to my Triangulated Group [06F36] – so I’ve used [06F36] to tag my AncestryDNA Matches in that Cluster. As it turns out, virtually all of the Matches I have under Thomas 1773 are tagged [06F36] – another indication of the power of Clusters. I can now really dig into the other [06F36] Matches (tagged at AncestryDNA and in the [06F36] Triangulated Group with 284 Matches from 23andMe, FTDNA, and MyHeritage) to find their BROWN ancestry.

James BROWN c1705-1776 [see diagram above] left a Will naming 16 children. Other than the given names, there are very few records to tie the surviving children back to James [we are dealing mostly with burned out counties in Colonial Virginia]. Very few on-line Trees are tied back to James. However, we have found families with the same given names as the children.  Isham BROWN is an example – same given name, but no records to link him to James, just a first name. But there are 2 descendants of Isham who are in Group 40 of the BROWN Y-DNA Project who claim Isham as their Most Distant Known Ancestor. Eake BROWN is a fairly unusual given name, and we are finding some records and descendants for him – looking for a living DNA Match… In his Will James named son George and George’s sons George and Archibald – two men in BROWN Group 40 claim a George and an Archibald (independently) as their Most Distant BROWN Ancestors… Theoretically we should be sharing about 2% of our cousins at the 6C level.  Yes, it’s a stretch, but it’s doable.  With virtually no good records, it might be the best avenue we have for linking these lines.

If enough folks try this process, we might get enough data to build probability curves and averages for the percent of shared cousins at different cousinship levels – a parallel to the Shared cM Project.


1. If you and a DNA Match can share your lists of Matches from a potential Common Ancestor, percent of Match overlap may indicate the cousinship level.

2. This takes work and time – I used it as a last resort, when my Ancestor left no records of children.

3. This is best done at AncestryDNA, with ThruLines, and therefor limited to 6C relationships, or closer.

CODICIL: In my excitement here I have presumed [06F36] is a BROWN Cluster or Segment. Not necessarily! I have concluded that [06F36] goes back to the Wilson BROWN couple – that [06F36] segment could have come from or through either Wilson OR his wife. It’s a 50/50 probability either way. I must do a lot of other analysis to figure that out.

[23_98Mb] Segment-ology: Percent of Shared Cousins Indicates Relationship by Jim Bartlett 20230315

Testing a Guess with Teamwork!


This is a developing story about a Brick Wall I’ve had for 48 years. My mother was a BAKER, and I know her ancestry back to the “Gunsmith” BAKERs in Pennsylvania in the late 1600s. My mother’s brother did Y-DNA to prove this line. One ancestor in the line was Elliott BAKER c1775-1836 who married Keziah BROWN in 1801 Prince Edward Co, VA. Keziah named her father as Wilson BROWN, Dec’d on the marriage license. In the 1850 census she stated she was born in adjacent Buckingham Co, VA. Sure enough in the 1782 to 1792 Buckingham Personal Property Tax Lists, there was a Wilson BROWN. In the 1793 PPTL, Wilson BROWN Estate was listed – Wilson had died. Skipping  over a lot of research and steps, I know: no one else has Wilson BROWN in their Tree(except my line); there are several different BROWN Trees in Buckingham Co, VA; adjacent to Wilson in most PPTL listings was an Isham BROWN (some DNA Matches, indicating he was probably a sibling, but no genealogy help); Wilson BROWN left no Will (or any documents naming wife or children). No known male-line descendants for Y-DNA. Dead end – Brick Wall.

In January 2023 a small group of us, decided to dig in.

1. We found a hitherto unknown 1776 Will of a James BROWN in nearby Cumberland Co, VA [credit Kevin Baker]. Note: There is a point that Cumberland, Buckingham and Prince Edward counties all touch – this is now the focus location. James’s will named 16 children, including Isham and Wilson. BINGO! I could find no one with this James in their Tree, despite several of his children with given names that recur in BROWN Trees in VA, NC, TN, KY, etc. But I did find a lot of BROWN Trees that had other, undocumented Ancestors about this generation – hmmm.

2. Another important find was linking Isham BROWN to the BROWN Surname Y-DNA Project – Group 40! Some BROWN Y-DNA experts [credit Bill Davidson] helped us rule BROWN lines in and out of consideration . This included several BROWN lines in Buckingham and nearby counties.

3. Two of the 16 men in Group 40 list Isham BROWN, born 1749, as their Most Distant BROWN Ancestor. They were sure of Isham, but could not determine his father – hmmm – the recently uncovered James? I can almost guarantee that if the 1776 Will of James BROWN had been easily found, many would have latched onto his son Isham [please excuse my cynicism].

4. If Isham was a brother of Wilson, then Wilson, and his male-line descendants (none of them known at this point), would also be Group 40.

5. Within the BROWN Group 40 were several lines back to the 1700s, but brick walled – and most of them were in this general area of Virginia.  My experience with Y-DNA Projects (I’m an Admin for 3 of them) is that American Y-DNA testers who form a family group, almost always have a Patriarch in America. In other words, it’s my expectation that there is a Patriarch of Group 40, probably in Virginia [I suspect James].

6. At least two of the 16 men in Group 40 list Thomas BROWN, born 1773, as their Most Distant BROWN Ancestor. Ancestry lists over 2,000 Trees for this Thomas BROWN (and his wife Nancy LITTON). Most have additional generations back, but with very sketchy documentation – pre-Revolution War records are hard to find in these counties. Communications with several Tree owners (not necessarily DNA Matches) revealed that they were unsure of Thomas’s father…

7. As it turns out, I have already found over 30 DNA Matches to this Thomas BROWN – ranging from 8 to 26cM – and I’m not even halfway through the list of possibilities. These DNA Matches span 7 of the 10 known children of Thomas – a good indication that Thomas is a relative of mine.

8. Looking back at the list of 16 children of James BROWN, and putting all the clues together, I estimate Wilson was born c1752 (3 years after Isham); and he probably had 9 to 10 children before he died (probably unexpectedly, without a Will) in 1792. Their birth years would be roughly c1773 to c1791.

Putting all of this together, my educated *guess* is that Thomas 1773 was a son of Wilson 1752; or a nephew. As a son, DNA Matches from him (and Wilson), would be 5th cousins (5C) to me. As a nephew, we’d need to go back another generation (to James) and the DNA Matches would be 6C to me.

How to figure this out? Use Teamwork to Test a Guess!

IF the relationship is “Thomas is son of Wilson,” then my DNA Matches to descendants of Thomas would also descend from Wilson and be about 5C to me. Going the other way, those DNA Matches should also have nominal 5C Matches to other descendants of Wilson, like my ancestor Keziah who married Elliott BAKER and had 8 known, surviving children with descendants who have DNA tested.

So I’ve asked such a DNA Match to please go to their AncestryDNA Match list and search for the surname BAKER, and see if some going back to Elliott BAKER (or any BAKER in Prince Edward Co, VA – there were several generations of this line there) show up as Matches.

An alternative is for me to list my 30 DNA Matches under Thomas. We expect to Match about 10% of our true 5C. So I’d expect any DNA Match from Thomas to also match about 3 of the same Matches. I have. A different DNA Match through Thomas should also match 3 of my Matches, but probably a different 3.

No need to go through the process of “Target Testing” when we already have a lot of known testers…

Testing a Guess With Teamwork!

This is a concept I’m working on – teamwork. I know it’s hard to get Matches to respond, so I’m hoping that a very clear, short objective, coupled with a relatively easy test process, would encourage a cousin to get involved. Particularly if the result would indicate new, more probable, Ancestor for them.

BOTTOM LINE – Form an educated *guess* and think of it as a given relationship. Then get widely spread DNA Matches from that added branch to look for DNA Matches in your branch.  Using daughter’s married Surnames makes this test even more precise. If you can get several to do this, and find their Matches in your branch – this would be very powerful evidence of a genealogy link. It seems to me that this is a particularly good process for common surnames, like BROWN. If you could also find Matches with DNA segments, you’d probably have a few Triangulated Groups – but that’s another story;>j

Wilson BROWN is my Ahnentafel 98 Ancestor. I plan to update this Brick Wall story as it develops.  Think about trying to get 2,000 folks to change their Trees…

[23-98Ma] Segment-ology: Testing a Guess With Teamwork! by Jim Bartlett 20230310

Distant Common Ancestor Couples


A Segment-ology TIDBIT

There has been some recent discussion about how far back autosomal DNA is useful. Some indicate the “practical” limit to be around 2xGreat grandparents (the 3rd cousin (3C) level). I put the word practical in quotes because I don’t believe the 3C level was intended to be a rock-solid/absolute limit. I think it was intended as recommendation for many genealogists – perhaps for most genealogists just getting started.

I’ve been a genealogist for almost 50 years. I have long since researched most of the available paper records. In the late 1970s, I worked for the Smithsonian, and spent my lunch hours scrolling microfilms at the nearby National Archives; or a weekly drive over to the DAR library to roam through their stacks. I look at DNA as a new tool to add more evidence to my existing Tree and extend it even farther.

I use segment Triangulation to group Matches and to build a Chromosome Map, which also informs about the contribution to my DNA from each generation of my Ancestors. But I also value what’s called genealogy Triangulation. This is when at least three of us (me and two widely separated cousins) agree on the same Common Ancestor (CA). For almost all of my known Ancestors, I have genealogy Triangulation well beyond two other Matches.

To document, and learn from, these CAs, I developed a CA Spreadsheet. See my Common Ancestor Spreadsheet blogpost for a description, a sample and a table of the columns. My CA Spreadsheet includes thousands of DNA Matches and their CA with me. For each Ancestor Couple, this spreadsheet documents way more than two Matches for genealogy Triangulation. It usually has many DNA Match cousins, all in a large genealogy “Triangulation” for each Ancestor Couple.

This spreadsheet also includes the Shared cM amount for each DNA Match. So, it is now easy to sum up the number of DNA Matches and the average cM amount for each generation:

The takeaways here include:

1. I have many DNA Matches in 5C, 6C, 7C relationships.  These stats are from my three grandparent’s Ancestors, almost all of them from Colonial Virginia – my maternal grandmother was a recent immigrant, and I get very few Matches on her line. [My parents were not related per GEDcom.]

2. At this distance, the cM relationships trend downward, as expected.

3. The averages are below 20cM.

4. For genealogy beyond the 4C level, I agree with the general concept to ignore the segment size. This is an analysis of genealogy agreement (Triangulation), that happens to be among DNA Matches. I am not claiming that the DNA segments, individually, “prove” each relationship. However, on average, some of the segments will be Identical By Descent, and when included in such large genealogy Triangulations, they increase the confidence that the genealogy is right.

5. Where known (or imputed), I also track the Clusters and Triangulated Groups (TGs) in this spreadsheet. There is usually only one or two Clusters indicated for each Ancestral Couple; and there are usually multiple TGs for each Ancestral Couple.

6. Disclaimer: Is my CA Spreadsheet 100% accurate? NO! Is it over 90% accurate? YES, IMO! Certainly the “story” in the table above is valid.

My MAIN OBSERVATION is that atDNA “works” beyond 4C.

How far back you want to take your genealogy is a very personal decision. You get to set your objectives. This post is to let you know the ability of atDNA to help you with Ancestors back at least to the 7C level.

[22BN] Segment-ology: Distant Common Ancestor Couples TIDBIT by Jim Bartlett 20230307

Small Segments Needed for Distant Ancestors


Segment-ology TIDBIT

To find bio-Parents we usually use Matches in the 90-300cM range. Grouping Shared Matches in this range usually gives us four Clusters – one for each grandparent. For a bio-Grandparent, we need to lower the threshold some to include third cousins (3C), and select the Clusters that would include the bio-Ancestor we want to find (in other words select-out the known Clusters). See my 2022 blog post: Finding Bio-Ancestors here.  That blog post includes a handy Crib Sheet to orient this kind of project. The Crib Sheet indicates the estimated number of Triangulate Groups (TGs) involved, but Shared Match Clusters also work. Since this is largely a genealogy project, using Shared Match groups (Clusters) at AncestryDNA is usually the best place to work on these projects.

For more distant bio-Ancestors, smaller cM Matches are needed. Try various cM thresholds, down to a 20cM threshold, and select the Clusters that point to your Target bio-Ancestor.

For even more distant bio-Ancestors, I subscribe to the concept of ignoring the cMs, and just focus on the genealogy. AncestryDNA only shows Shared Matches down to 20cM, but Clustering can be done at the other companies, down to small cMs. Grouping by segment Triangulation can also be done, and then selecting the TGs that point to the bio-Ancestor.

If you get a hint of a surname, or a specific geography, you can search your Matches at AncestryDNA, to find under-20cM Matches that may have Shared Matches – indicating the Cluster they would be in.

For 4x to 7xGreat grandparents, many of the Match cMs will be under 20cM. Remember this is a genealogy project – the cMs don’t matter.

In all projects looking for (or even just confirming) a bio-Ancestor – let our Matches identify you Ancestor, by determining their Common Ancestor – see the link in the first paragraph.

The main point of this blog post is that Matches with small segments are needed to work on distant Ancestors.

[22BM] Segment-ology: Small Segments Needed for Distant Ancestors TIDBIT by Jim Bartlett 20230306

Triangulated Group Analysis


Segment-ology TIDBIT

Let’s analyze a generic Triangulated Group (TG).  There are several facets to this analysis…

Facets related to me:

1. My DNA segment – A Triangulated Group (TG) “segment” is a specific segment of my DNA. It is defined by a Chromosome number, start and end positions, and the total Mbp. The number of SNPs included and the cMs can be obtained through look-up tables on the internet (I have not done that).

2. TG Ancestor – A TG segment of my DNA first came from a specific Ancestor of mine. I’ll call this the TG Ancestor. This TG segment was passed down through descendants of the TG Ancestor, to one of my parents and then to me. All of my Ancestors who descended from the TG Ancestor also had that TG segment in their DNA. NB: the TG Ancestor started with a full Chromosome (a big segment) which he/she passed down – the TG segment was part of that larger segment/Chromosome. This original larger segment was then whittled down through the generations, but each generation had, at least, the full TG segment. NB: A segment may be passed down, one or more generations, intact (i.e. no whittling down), but the TG segment is always intact from the TG Ancestor down to you.

3. TG segment origin – The TG Ancestor received the TG segment (usually a larger segment) through a recombination process. His/her parent recombined DNA from their two parents to create a new chromosome to pass to the TG Ancestor. At this point, in our TG Ancestor, our TG segment is made up of parts from the TG Ancestor’s parent’s two chromosomes – one from each of the TG Ancestor’s grandparents. Thus, this whole TG segment did not exist, on one chromosome, in one person, before this time. The TG Ancestor is the first person to have this particular TG segment.

4. Logic – Matches who share this full TG segment, should also share this Common TG Ancestor – because this TG segment is unique to this TG Ancestor. [It can be argued through logic, that there is a possibility of this exact same segment being created in another person – granted. But the odds are extremely low, and even more distant when you consider this happening in the small subset of your DNA Matches in a TG]

Facets related to Matches and *shared* segments:

5. Cousin segments – In general, our cousins will get somewhat different segments than we do from our Common Ancestors. Apply #2 above to a Match. Our Ancestor passed down a chromosome to their children – some of it identical, some different. The DNA segments passed down through their children and their descendants to our Matches will be randomly different. What we see through a DNA test, is the overlap created by shared DNA segments – the part of our DNA from a Common Ancestor that overlaps. We might get Chr 06: 53-86Mbp and the Match may get Chr 06: 64-97Mpb – the “shared segment” is the overlap: Chr 06: 64-86Mbp.  Our segments from Ancestors are rarely the same as our Matches’ segments from the same Ancestors, but

5. Cousin segments – In general, our cousins will get somewhat different segments than we do from our Common Ancestors. Apply #2 above to a Match. Our Ancestor passed down a chromosome to their children – some of it identical, some different. The DNA segments passed down through their children and their descendants to our Matches will be randomly different. What we see through a DNA test, is the overlap created by shared DNA segments – the part of our DNA from a Common Ancestor that overlaps. We might get Chr 06: 53-86Mbp and the Match may get Chr 06: 64-97Mpb – the “shared segment” is the overlap: Chr 06: 64-86Mbp.  Our segments from Ancestors are rarely the same as our Matches’ segments from the same Ancestors, but the TG segment is always intact from the TG Ancestor down to your Match. Always be mindful of the difference between your own DNA segments, and a “shared segment” with a Match.

6. Cousins on the TG Ancestor – these Matches may share roughly the same amount of DNA as the full TG segment, but some may well share smaller segments. It all depends on the recombinations that occurred in the generations between the TG Ancestor and the Match. Matches in a TG are already analyzed to share at least part of the TG segment with you and with other Matches.

7. Closer Cousins – these Matches also may, or may not share the full segment. Actually close cousins may share somewhat larger segments with us – beyond the scope of the TG segment. This indicates these closer cousins share more than one TG with us and a closer Common Ancestor. However, this closer Common Ancestor would have to be a descendant of the TG Ancestor. Maybe the closer Common Ancestor would be a grandparent or Great grandparent.  

8. Distant Cousins – Other Matches in the TG group may share smaller segments and be related through a more distant Ancestor of the TG Ancestor. Refer to #3 above. We could have a Match cousin related through a parent or grandparent, etc. of the TG Ancestor. In this case the Match would have only received the smaller DNA segment that was part of the full TG segment in the TG Ancestor. It is probable that Matches sharing small segments (in my case down to my 7cM threshold), could be cousins way beyond my genealogy horizon. This is particularly true with pile-up regions within a TG. The whole TG segment may come from a TG Ancestor well within my genealogy horizon, but the pile-up Matches are much more distant (or potentially false segments – a different story).

Summary – the Matches in a TG group can be cousins from many different generations, but all on the same ancestral line. The best estimated guess of relatedness to a TG segment would be a look-up of the cMs and then refer to the Shared cM Project. Generally on Chr X, the relationships may be further back.

Remember a TG segment represents your DNA – only your DNA – your DNA Matches will have a different TG.

[22BL] Segment-ology: Triangulated Group Analysis TIDBIT by Jim Bartlett 20230110

Review The Comments


A Segment-ology TIDBIT

I’d like to encourage all “Segmentologists” to periodically review the comments to my blog posts. I try to respond to every one of them and often go into more detail and/or provide suggestions for specific issues. If I may say so, there are often some more gems in the comments – including feedback from followers of this blog. I recently got a comment and elaborated on a post from over 7 years ago…

[22BK] Segment-ology: Review the Comments TIDBIT by Jim Bartlett 20221213

Sibling Crossovers


The question came up about siblings sharing the same crossover points. The answer is yes – some of them will be the same. Let’s look at this generation by generation. [There is often good discussion in the Comments to these blog posts – we are all learning on this journey. As a result of a recent comment, I decided to do a blog post about this topic]

The set-up:

1. One genome – let’s use our Mother’s side – 23 Chromosomes

2. Assume the average of 34 crossovers per generation.

3. A crossover is the point where DNA changes from one grandparent to the other grandparent, when the mother recombines her two chromosomes into a new one to pass on to a child.

4. Crossover points are random.

Mother’s DNA already has crossovers created by many of her Ancestors. She will recombine the DNA from her two parents at 34 places over the 23 chromosomes, and pass these new chromosomes to a child. Note: this means usually 0, 1, 2 or 3 crossovers per chromosome (on average 1 per 100cM). Since these crossovers are randomly formed for each egg, it would be rare for any of her children to have the same crossover from her.

The 34 new crossovers created 34+23=57 segments. These 57 segments “cover” all 23 chromosomes, from beginning to end of each one. These 57 segments are from Mother’s parents – our grandparents. All the crossover points from recombination events in prior generations are fixed (static) in the two grandparent’s DNA.

Example: Mother’s paternal DNA on Chr03 – from 47Mbp to 123Mbp has a crossover point at 68Mbp. Each of Mother’s children who got her paternal DNA that included the point at 68Mbp would include that crossover point. Mother could pass a paternal Chr03 segment 47-83Mbp to one child and paternal Chr03 59-119Mbp to another child – both of these children would have the same crossover at 68Mbp.

Note: The 68Mbp crossover could have occurred at the great-grandparent generation, OR at some previous generation.

This is a good example of why Chromosome Mapping *by generation* is important. In general Segment Triangulation results in Triangulated Groups (TGs) from different generations of ancestors. The TGs are not all from 4xG grandparents, or any other specific generation. However, if you have the Common Ancestor (CA) for your TGs, you can easily build a Chromosome Map for different generations. In my case I have 372 TGs – I know the CA side and grandparent for almost all of them – they roughly “fit” into about 114 groups (representing my 4 grandparents on both sides) on my 45 chromosomes.

Bottom line: Siblings won’t (generally) get the same crossover points from their parents, but likely will share some crossover points from grandparents and more distant Ancestors.

[05F] Segment-ology: Sibling Crossovers by Jim Bartlett 3 Dec 2022



I wanted to share one of the huge benefits of WTCB. I’ve pretty much completed the WTCB down to 20cM Matches and have added in a number of under-20cM Matches for which I had segment data (from GEDmatch, primarily, and some who had tested at the other companies). These under-20 Matches can be Clustered by looking at their over-20 Shared Matches for a consensus.

There are positives and negatives to WTCB. Overall, a large percentage of the over-20 Matches fit into very solid Clusters. But, just like a distribution curve, some of the Matches do not have many Shared Matches (a few have 0), and some just don’t seem to form a good, solid consensus. If you know me, I focus on what I *can* do – so I want to give you an example of a successful Cluster. And I want to note that this is not the best example, but it is a good one.

Here is a picture of Clusters 54 to 79 in a Super Cluster. The 281 Matches in the Super Cluster range from 20cM to 56cM (the upper threshold was 60cM for this run).

In my review of most of the Clusters and SuperClusters, I’ve found that the individual Clusters look prettier and more solid, but they do not represent a split in ancestral lines within my genealogical time frame (roughly 9 generations back; 8C level). So I have combined most of them into Cluster 54 – a total of 281 Matches.

In this Cluster I now have 3 Matches with an MRCA of A0020 (MITCHELL/UNDERWOOD couple); 12 Matches with an MRCA of A0084 (UNDERWOOD/CANNADAY) and 27 Matches with an MRCA of A0170 (CANNADAY/HILL). I also have 4 Matches who have MRCAs on different lines. The Cluster is very solid, so I suspect these 4 Matches are probably *also* related to me somewhere on my MITCHELL to UNDERWOOD to CANNADAY line. But clearly the 42 Matches on one line show a consensus!

Also within Cluster 54, I have 9 AncestryDNA Matches with segment data – they are all in Triangulated Group [17D25] – another pretty clear consensus. In DNA Painter, I could paint all 281 Matches on Chr 17, from 24 to 45Mbp. Note: In my TG spreadsheet I have over 150 Matches in TG [17D25] – 9 of them from Ancestry Matches and the rest from the other companies.  

I have Ancestors in my Tree beyond A0170 (CANNADY/HILL) which are fairly well known and also in many other Trees, and I’ve found Matches with those more distant MRCAs in other Clusters, but not in this Cluster 54. I’m coming to the conclusion that the 21Mbps in [17D25] probably came to me from either William CANNADAY 1730-1801 (A170) OR his wife, Nancy HILL 1733-1801 (A171).

But the best is yet to come. This Cluster 54 is a classic *pointer*.  I am now pretty sure that the rest of the Matches in this Cluster will have an MRCA with me on the same line. In fact, I’ve only recently found several of the MRCA Matches by building Trees back and/or looking at Unlinked Trees. Here is an example:  

In Cluster 54, I had a 36cM Match with an Unlinked Public Tree with 6 people in it. I opened it up to find only one real lead – Audrey (so I searched Ancestry for her):

BINGO! Note Audrey’s mother is a CANNADAY!! The rest was easy – I quickly found the Match’s link to A0170 (CANNADAY/HILL).

Note: I’ve had others that were just as easy; and some that took more searching and digging; and some that I threw in the towel and moved on.

The bottom line is that the WTCB tool can be very valuable in many cases. And when it works, I’ve got a Cluster which is a great MRCA-focused tool; I’m compiling consensus data for the Cluster (firming the TG and Chromosome Map), adding to the Ancestry Match Notes and helping ThruLines find more MRCAs in Private Trees.

[19Nc] Segment-ology: WTCB SITREP Nov 2022 by Jim Bartlett 20221112

WTCB Issue – Alt MRCA


I have a number of cases where the Match has an MRCA, but Clusters with a different group of Matches who clearly have a different MRCA and/or TG.  Example: A Match who has an alternate MRCA which doesn’t align with a TG. I discount the MRCA because the shared DNA segment with the Match could not have come from that MRCA. Some have a paternal TG and a maternal MRCA; some are clearly from different grandparents on the same side. I now have found two examples of such a Match who Clusters with other Matches who share the MRCA but not the TG. It is not unusual for a Match to have more than one MRCA from Colonial Virginia, but usually one is closer and the closer MRCA has a much higher probability of being the one who passed down the shared DNA segment. But “higher probability” does not mean always.  

My latest example is a Match with TG [01Y36] 14.0cM (on my mother’s side], but over half of the 23 Shared Matches have TG [17D25] (on my father’s side). [17D25] is a pretty well-established TG for me with an MRCA of A0170P (my CANNADAY/HILL ancestral couple at the 6C level). So I checked my Notes and found the Match has a ThruLine to CANNADAY/HILL. That explains why the Match Clusters with other Matches with MRCAs of A0170P.

Bottom line: Although my main objective is deep Chromosome Mapping, the ultimate goal is to get the genealogy right. In this case I want to also figure out the [01Y36] MRCA, so I must remove this Match from the A0170P-[17D25] Cluster. I also have to remind myself to follow the data – the data is talking to me, I need to listen…

[19Nb] Segment-ology: WTCB Issue Alt MRCA by Jim Bartlett 20220926

Segment Data for Ancestry Matches 2


A Segment-ology TIDBIT

My first post with this title (here) listed 4 ways to get Segment data for AncestryDNA Matches; and then added another way using GEDmatch.

Here is yet another way.

In Walking The Clusters Back (see WTCB 2022 and WTCB SITREP) I’ve now completed the analysis of all Matches over 20cM – almost all fit into one of several hundred Clusters. I’m now integrating the below 20cM Matches who have segment data (a TG ID), usually from GEDmatch – over 800 of them. Most of them have Shared Matches which usually provides a consensus on the Cluster.  In checking my Master segment spreadsheet (with all of my Match Shared Segments), I noticed a number of AncestryDNA kits which didn’t yet have a link to an Ancestry profile. It turns out that usually all the Matches with the same TG ID will be in one Cluster. It is a relatively easy task to find that Cluster (particularly with WTCB) with some of the Matches – and then review the few other TG Matches with the other Matches in that Cluster. I usually send a message to the Ancestry Match to confirm they indeed uploaded to GEDmatch (and promise to help them with the DNA if they are).

Result: more AncestryDNA Matches linked to specific DNA segments (TGs).

[22BJ] Segment-ology: Segment Data for Ancestry Matches 2 TIDBIT by Jim Bartlett 20220223