A Segment-ology TIDBIT

Subtitle: Filter Your AncestryDNA Match List

Bottom Line Up Front: Filter your AncestryDNA Match list by cMs when your objective is a distant Ancestor. Also use Side and Surname filters to further reduce your Match list for review.

Most of us use the Shared cM Project to look up the Shared cMs of a DNA Match to see the possibilities of our relationship. We’ve learned that 3,500cM means a parent/child relationship; 2600 cM is a sibling; 1750cM is a small group of close relatives; 880cM is often a 1st cousin (1C), or other close relatives. And we understand that as the shared cMs get smaller, the range of possible relationships expands.

But we can use the Shared cM Project in the opposite way – what is the probable shared cM for a given relationship? We see narrower ranges for close relationships, and fairly wide ranges for more distant relationships. However, even though the range may be relatively wide for distant relationships, the average cM does shift down as the relationship gets more distant. For example, a 3C relationship would not have more than 234cM; a 7C would not share more than 57cM (and the average for a 7C is 14cM).

Suppose we are focused on a particular Ancestor in our Tree. Our Target could be a brick-wall Ancestor; or a potential NPE (Not the Parent Expected) Ancestor; or a suspicious Ancestor; a known Ancestor for whom we’d like to find a new cousin who has some in-depth knowledge of that family; etc. We can use the Shared cM Project to narrow down our search! This works for close relationships as well as distant ones – my focus here is on the distant ones, but the process is what is important.

A good site to use the Shared cM Project is at DNAPainter: https://dnapainter.com/tools/sharedcmv4 – this site provides a number of interactive tools along with the basic Shared cM chart. For example, a 5C relationship (back to a 4xG grandparent – we have 64 of them) would average 25cM – and 50% of them would be in the under-20cM range. In this case we might want to start with the 50% in the over-20cM range. But for a 6C relationship (for 128 of our Ancestors) the average is 18cM and 70% of the Matches will be in the under 20cM range. Each of us gets to pick our own objectives and projects to pursue. If yours is like many of mine and beyond the 5C range, working within a range of cMs may be helpful.

Here’s how. At AncestryDNA, open up your list of Matches, and look at the row of “Filtered by:” tabs – we can use many of these in combination.

For this example I’m going to use the Shared DNA tab to select a range of cMs, AND the Groups tab to select my Maternal side.

In the project I’m working on, I’ve already looked at the Matches down to 16cM. By selecting a range for the next search, I also speed up the time for AncestryDNA to produce my filtered list of DNA Matches. In this case I’ll be looking at 11cM to 15cM. Remember to Click on Apply!

I’ll also filter my list by using the Groups tab to restrict the list to only Maternal-side DNA Matches:

In this case, I’ve chosen the Maternal side (remember to click on Apply). This will filter out a lot of Matches that don’t really apply to my Target Ancestor [I can later select the “Unassigned” Group to check those, too.]  Note that you can ALSO select several categories under Custom groups – such as New Matches (especially helpful if you want to revisit this project at a later date to check on new Matches), and/or any of your “dotted” Match categories (not much help in my current project because I’ve already visited – and dotted – all of those Matches I could determine, and I’m looking for new ones now in the under-20cM range.) In some projects, this “dotted” filter may be valuable.

And there is one more filter I often use. For my current project, I am looking for my DNA Matches who have a BROWN Ancestor. So, I click on the “Search” tab, which brings down a row of options. I type BROWN into the “Surname in matches’ trees” search box:

You can decide to check the “Include similar surnames” box, or not. For this project, I got plenty of results with just BROWN, and, if I wanted to, I could go back and try BROWNE or BRAUN, etc. I’ve had mixed results with the “Birth location in matches’ trees” filter box – sometimes the result is either the surname or the location, and I’d be wanting both. I did have very good results on a project with HIGGINBOTHAM surname and Amherst County, Virginia location. You might need to try some combinations to see which works the best for your project. Remember to click on the blue, highlighted Search box to include this filter.

This process of filtering is a powerful way to shorten your list of DNA Matches, tailoring them to your project goals. The addition of a cM range has helped me focus on more distant Ancestors and to speed up the AncestryDNA listing algorithm.

BOTTOM LINE: When you are searching for DNA Matches, think about the best way to combine the filters (including a cM range) and search parameters at AncestryDNA.

[22BT] Segment-ology: Using the Shared cM Project in Reverse TIDBIT by Jim Bartlett 20230601

A Segment-ology TIDBIT

Bottom Line: We cannot tell from a single Match; but there are at least three ways to figure it out.

SETUP: One cousin, or even several cousins, who share a Most Recent Common Ancestor (MRCA) with us. The “Common Ancestor” is really a Common Ancestor “Couple” – usually a husband and wife. You descend from one child of this couple, and the matching Cousins descend from one or more of their other children. The question comes up, which parent passed down the DNA segment to us? From this data, we cannot tell which parent passed down the DNA. All we know is that one or the other parent passed it down. I know of three ways to figure this out – maybe you know of additional ways…

1. Grouping *to* the parents’ parents. One DNA Match-cousin back to the MRCA won’t do it. We need a group of Matches – at least one back to the MRCA, and other Matches – often with smaller shared segments – that go back another generation. The group can be formed via Clustering (grouping Shared Matches); or segment Triangulation (or DNA Painter). The goal is to find a Match in the group who is a cousin at least one generation farther back than the MRCA. This will almost always tell you which side of the MRCA the DNA came from. Note: there is a very low chance, this might not work, but finding more than one more distantly related cousin on this line adds insurance. It is best to do this with segment Triangulation which represents a single DNA segment going back, but Clustering works, too. As you find more and more Matches with the MRCA, eventually (with smaller cM segments) they will break into two groups, one for each parent in the MRCA. Each of these groups will be based on a different DNA segment (a different subset of a Triangulated segment, involving smaller shared segments).

Note this is really a subset of Chromosome Mapping, and/or Walking the Ancestors Back.

2. Different partners. If one of the parents had children with a different partner (married or not), and the other Matches descend from this other partner, then you know the shared DNA segment had to come from the Ancestor who had multiple partners – the same DNA could not have come from different partners.

3. Differing ethnicities. If the two parents in an MRCA have very different ethnicities overall (or you can tell the ethnicity is different for this specific shared DNA segment (usually a TG segment), then a review of the Matches’ ethnicities might indicate which one passed down the DNA.

As with many things in genetic genealogy, the DNA may throw you a curve ball. I’m old enough to remember the Mickey Mouse Club on TV – and the “anything can happen day”. As you continue on your genetic genealogy journey, the evidence will mount. It should all point to the same results – which match your unique Ancestors and DNA segments.

Feel free to use this blogpost as a way to answer this recurring question on-line.

Amended slightly to call out the different partners as one of three ways.

If you have a favorite method of figuring this out – please post in the comments.

[22BS] Segment-ology: Does the DNA Come from the MRCA Father or Mother? TIDBIT by Jim Bartlett 20230515

There are, generally, two discussions about this.

1: One is the MRCA is really a couple – and both your and your DNA Matches descend from this MRCA (couple). You descend from one child of the couple, and your Matches descend from other children of the couple. We may not know which individual in the couple passed down the DNA we share, but we do agree it’s from one or the other.

2: The other discussion is that the child of the couple that you descend from had to have the DNA segment and is then *the* MRCA (singular). But, at least in my mind, this MRCA (singular) is not the MRCA of the Matches, and things get a little complicated trying to have a discussion among the Match-cousins. The various MRCA (singular)s are not “common” to the various Matches.

In Segment-ology, I use MRCA to mean MRCA (couple). This couple is common to Matches who descend from them.

[22BR] Segment-ology: How to Define the Most Recent Common Ancestor by Jim Bartlett 20230513

Small-segment Matches (<15cM) with conflicting Shared Matches (no consensus) are probably false.

This Observation/Theory comes from two directions:

1. Science and observation tells us that (A) almost all Shared DNA Matches (Matches) >15cM are true; and (B) to varying degrees, some Matches below 15cM are false. There is a distribution curve which has a small percentage of 14cM Matches as false, down to about half of 7cM Matches are false and larger percentages of even smaller segments are false. It’s hard to sharpen this marshmallow of data, so please grasp the overall concept that as the cMs decrease below 15cM, the percentage of false Matches increases to areas where most Matches are false.  And don’t be confused – you can have a true Common Ancestor with a false Match – it’s just that there is no DNA link (or “proof”). In fact, most of our true 4th cousins (4C) and greater will not be DNA Matches at all. Another point is that there is no such thing as “partly true or false” – the shared DNA segment is all true (from a Common Ancestor) or all false (not from a Common Ancestor). Please don’t go down the “rabbit hole” that *part* of a small segment may be true – we are already down to small segments, even tinier segments aren’t a step in the right direction, unless you have a very, very special case. Not the thrust of this blogpost!

2. My observations of Matches under 20cM shared segments as I search/analyze this huge group (80,000) for Matches with a BROWN Ancestor – also a huge subset (thousands) of my under 20cM Matches.

Background 1: I’ve done the “homework”. Using the Walking-The-Clusters-Back process (starting here), I was able to identify hundreds of Clusters to specific parts of my Ancestry. Almost all to a parent; 98% to a grandparent; roughly 90% to a Great grandparent; etc. out to some that were tagged to 7xG grandparents (8C level). Overall, I have in my AncestryDNA Notes for almost all over-20cM Matches, *some* indication of their line in my Ancestry. Most of these have also been tagged to specific Triangulated Groups (TGs). Part of my analysis of the under-20cM Matches is a check of their over-20cM Shared Matches. Most have some Shared Matches. Sometimes, an under-20cM Match will have many Shared Matches in consensus – most in the same Cluster or TG. Sometimes they will not.

Background 2: My BROWN Project. For this project, I filter my Match List by Maternal (the side for my BROWN line), a cM range (ie: 12 to 13cM); and the BROWN surname. I then look at each Match, and put something in the Notes box…

Background 3; Keeping Track.

[“Good” Matches] I’ll add (ie: impute) the Cluster/TG to the Notes for each concensus Match. Note: some of these will be a consensus on the BROWN line; some will be a consensus on some other line. I also add a Note about the oldest BROWN I’ve found for each of these Matches, if it’s likely to tie to my BROWN line – a judgment call.  

[When I’m finally done ferreting out all of these lines in a consensus BROWN Cluster and/or a good probability of a link to my Tree, I’ll look at the number of Matches in each family group, and really dig into the research – this is sort of like collecting clues in Quick-and-Dirty Trees to see what’s worth pursuing.]

[“Iffy” Matches] Some Matches don’t neatly fall into the Good or Bad category – I look at them and usually build their Tree back far enough to determine if a tie-in to my Tree is possible – judgment call.

[“Bad” Matches] I add a Note to Matches with no Shared Matches: ”SM:0”. And I add a Note to Matches with various, conflicting Shared Matches (often on both sides): “SM – var”.  

Observation 1: Research/Tree building for Matches with “SM:0” and “SM – var” Notes almost always went nowhere. They had a BROWN Ancestor (a search filter), but their BROWN Ancestor was from England or Scotland or New England, etc. Clearly a very low probability of linking to my BROWN line in Colonial VA. For these Matches I added “X BROWN” in the Notes to remind me they’ve been looked at and discarded.

Observation 2: Finding a Match with consensus Shared Matches that had known/suspected BROWN Clusters/TGs was a BINGO! They *almost always* had BROWN Ancestry that linked to mine – whether it was in their Tree or in the Q&D Tree I built out for them. Some of the iffy Matches which had a few Shared Matches with favorable BROWN Clusters/TGs, but not a consensus, turned out to link to my BROWNs. Some did not.

In my BROWN project, I’m done with the 11cM to 19cM DNA Matches and am part way through the 10cM Matches – a lot still to do. I wanted to record my observations that DNA Matches who had a BROWN Ancestor pretty easily fell into probable/possible vs “no way” categories. And my growing belief is that Matches with “SM – var” are probably FALSE Matches – not going to be a genetic cousin on any line.

BOTTOM LINE: Matches under 15cM with various conflicting Shared Matches are probably FALSE. Certainly, to be culled out to focus on Matches who have a clear consensus of Shared Matches on one line. This is *not* a guarantee, nor does it mean all other Matches are true. But given the shear number of BROWN Matches to go through, I’m going to begin using this theory as a “TRIAGE” method. It’s the only way I can get through this BROWN Project.

[22BQ] Segment-ology: How To Detect False Matches Theory by Jim Bartlett 20230506

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?

SMALL SEGMENTS!

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

A Segment-ology TIDBIT

A Triangulated Group (TG) has two meanings – segment and group.

Segment – A TG represents a segment of DNA. A TG is defined as a Start Position and an End Position on one Chromosome (on one side – Paternal or Maternal). It describes one part of your DNA – accurate between two cross-over/recombination points*. Thus, a TG is a long string of SNPs on one chromosome – it is phased data on one side or the other. If we were to compare the raw data from each of the Matches in a TG, we’d see that they all had the same value at each point.

Group – A TG is also a group of your Matches. Each Match shares a phased DNA segment with you** that came from one of your Ancestors***.  All of the Matches should share the same Common Ancestor (CA) with you.***

Hedging a little…

* There is no “sign post” in our DNA to indicate the cross-over points, and the matching algorithms cannot exactly determine the start/end points of a segment – they may start before, and/or end after, the real ancestral segment. But they are pretty close. I say the segment ends are “fuzzy” – but the bulk of the TG segment is definitely from one Ancestor.

** It is possible that some Match(es) may have a false segment that happens, by chance, to match the phased string of SNPs – virtually always a segment under 15cM. If this Match/segment is critical to you, the Match can Triangulate at that location to determine if the segment is true or false.

*** The segments that pretty much cover the TG segment should be from the CA. Smaller segments that appear to be from one end or the other of the full TG segment, may well be from Ancestors beyond the CA. Note this is often the best way to determine which parent (in a couple) the DNA segment came from – the more distant Ancestor would be ancestral to one or the other of the couple.

Usually the TG meaning can be gleaned from the context – is the author talking about segments or Matches. If it’s not clear – call the author (often me) out!

[22BO] Segment-ology: The Two Meanings of TG TIDBIT by Jim Bartlett 20230407

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.

BOTTOM LINES

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

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

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

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