A Segment-ology TIDBIT

There are several key elements of good genetic genealogy – I’m going to call them Gold Stars.

1. DNA Match – as designated by the testing companies and GEDmatch. Most of these are our genetic cousins. I have a lot of them (over 120,000); and they are a good subset to work with. Worth a Star.

2. IBD Segment – We generally assume that virtually all Matches above 15cM have true genetic links; and my analysis is that about 66% of those 8 to 15cM are also true. Granted, some of the under-20cM Matches will be beyond a genealogy time frame (about 9 generations for me), IBD gets a Star.

3. Common Ancestor – This is a primary goal of genetic genealogy – finding a Common Ancestor with each Match. Notes: some Matches will have multiple CAs within a genealogy timeframe; just finding a CA does NOT necessarily mean that the Shared DNA segment came from that CA; a Match may share multiple DNA segments, and possibly multiple CAs. So finding a CA is worth a Star.

4. ThruLines (and Theory of Family Relativity) – I’ve found these to be over 90% correct. If you agree with them – add a Gold Star.

5. Same side – Ancestry and FamilyTreeDNA now indicate the “side” that each of our Matches is probably on. So far, I think this process is pretty accurate. The Common Ancestor should agree with the “side” for a Gold Star. If there is not agreement with the side, there may an additional Common Ancestor with the Match (on the same “side”]; or the “side” may be incorrect.

6. Paper Trail – each Common Ancestor should be supported by good genealogy paper trail of solid records. Not always possible; but add a Gold Star if you can document your and your Match’s paper trails.

7. Segment Triangulation – indicates your DNA segment is an IBD (true) shared segment; and probably the Matches’ segments are too. A Gold Star.

8. Shared Matches – [aka In Common With; Relatives in Common]. If most of the Shared Matches are in agreement, add a Gold Star.

9. Clustering – tends to group DNA Matches on an Ancestor. If the consensus of Matches in a Cluster is an Ancestor (or even 2 or 3 in an Ancestral line), add a Gold Star.

10. Reasonable Tree – does the Match with a Common Ancestor have a reasonable Tree? If a Match has a Tree with just one descendant (the Match’s Ancestor), that is a warning signal [NO Gold Star]. If a Match has a Tree with way too many children, given names repeated, different children with same birthdate – this is probably a research Tree with a collection every possible child – sometime born at many different locations – warning-warning! This is very flimsy evidence (NO Gold Star]. However, if the Match’s Ancestral line shows a reasonable number of children, spaced 1 to 3 years apart, that is a good sign. Alignment with census records is a plus. Use judgment to claim a Gold Star.  

Ideally, we’d have 10 Stars for each Match – but, that ain’t gonna happen very often… And I probably won’t be adding a Star # in my Notes. But I do review most of these when I accept a Match with a Common Ancestor. I just thought I’d share my compilation of thoughts when I find a CA.

This may be an imperfect list, but I hope it is helpful. Improvements/suggestions are welcomed in the comments. This Gold Star concept is not a set of hard rules – it’s intended to be helpful ideas. Your judgment should be the final say for your genealogy.

Note for genealogists – our genetic cousins are a small fraction of all our true cousins. I often add individuals to my Tree who are not DNA Matches.

[22CD] Segment-ology: Gold Stars TIDBIT by Jim Bartlett 20231229

A Segment-ology TIDBIT

What if the genealogy is correct but the shared DNA is on the other side? Discard because the relationship is not from the Ancestor who passed down the DNA segment? Save because we are in fact real cousins, despite the DNA? Most of our real cousins beyond 3C won’t share enough DNA to be designated as a Match.

Same quandary with a Match sharing one DNA segment, but related two ways. Both ways cannot be through the same segment.

Now that Ancestry shows “sides” (Maternal/Paternal), I’m finding that some of the ThruLines are not on the same “side”.

Sometimes this happenstance leads to finding a genealogy error and/or finding another genealogy relationship which is compatible with the shared DNA segment – sometimes not.

With almost 50 years of genealogy research under my belt, I’m very reluctant to “discard” any true relationship. I worked for 35 years finding cousins before atDNA testing came along – I’m not going to trash tens of thousands of cousins just because they don’t share DNA with me. They certainly share Ancestry with me – and records and stories and friendships.

On the other hand, my current quest is a deep Chromosome Map – linking my DNA segments to my Ancestors. Sort of a “who is responsible” for each of my quirks. A relationship that is not based on a DNA segment, is a distraction at best… a wrong rabbit hole… a misdirection… an error!

I think the solution is to keep all the findings, but clearly mark the genetic genealogy ones.  What is your take? Please leave comments.

[22CC] Segment-ology: Quandary TIDBIT by Jim Bartlett 20231224

A Segment-ology TIDBIT

When reviewing Ancestry ThruLines (or any potential Common Ancestor), go for the Triple Play!

Make sure the Common Ancestor AND the Side (Maternal/Paternal) AND the consensus of Shared Matches are all in agreement. If the CA is correct, they should be. Or at the least, there shouldn’t be a large conflict. I am finding a number of ThruLines under 15cM which do not agree with the Side. It is entirely possible to have a genealogy relationship (per ThruLInes) which is not the same as the genetic relationship (I believe most of the “Side” designations are valid). This would mean there is also another Common Ancestor that agrees with the Side – entirely possible for my Colonial Virginia ancestry. Or the Side could be wrong…

In any case, when you don’t have a Triple Play, it calls for some extra thought and/or research.

Just saying…

[22CB] Segment-ology: Go for the Triple Play! TIDBIT by Jim Bartlett 20231220

A Segment-ology TIDBIT

A question recently came up: Are the Ancestors on two sides of a crossover point, always a mother and father (in either order)? Or: If I know the Common Ancestor (i.e. the father or the mother of the TG couple) of a TG segment, must the next TG segment be the other parent of the TG couple.? The answer is YES, with an important caveat: only when we are talking about mother and father of our Ancestor who created the crossover.

Important scientific fact: A crossover is formed when a human recombines two Chromosomes to create a new Chromosome that is then passed to a child. One of the two Chromosomes is from the Mother, and the other is from the Father. So one parent is on one side of each crossover, and the other parent is on the other side of the crossover.   Here is Figure 6 from my 2015 blogpost: Segments – Bottom Up:

Note: each of the Chr 05 lines above is your Maternal Chr 05 – it’s just broken down for each generation. In the Grandparent look, the two crossovers were created by the parent using grandparent segments (assuming an average of 2 crossovers per generation for Chr 05). Note the Ahnentafel numbers to represent generic ancestors – even numbers are males, odd numbers are females. The first crossover created by the parent shows 7 & 6, or female & male, on the two sides of the crossover. When the first grandparent segment ends at the crossover, the next segment is the opposite parent. The second crossover created by the parent has 6 & 7 (male & female) on the two sides of the crossover.

The next line – the Great grandparent look has 2 more crossovers – created by the grandparents, when each of them recombined their respective 2 Great grandparent chromosomes. One of the crossovers is between 14 & 15 and the other between 13 & 12 (there was no crossover when the Ancestor 14 segment was passed to daughter 7). So again, each new crossover has a male and a female (in some order) on the two sides of each crossover.

Check out the two crossovers (on average) added at each of the next two generations – they all have the mother on one side and the father on the other side of the crossover.  Note carefully the word “added” (or created or formed).

Now here is the catch… In the Great grandparent look above, the last crossover has 12 & 14 on each side – two males. This seems to contradict the basic concept. And if we were applying the basic concept to TGs at the Great grandparent level it would be wrong. What’s up? Well, what looks like a crossover between Ancestors 12 & 14 is in fact a crossover – but it was formed by Ancestor 3 when she recombined Chr 06s from her parents 6 and 7 – these are the two parents of the ancestor who first formed (or added or created) the crossover.

When we form Triangulated Groups (TGs), we use groups of overlapping segments. But there is nothing in the TG criteria about the generation of the TG. We do understand that the TGs start and end at crossover points – when we shift from one Ancestor’s DNA to another Ancestor’s DNA. But until we can Walk the Segments Back (generation by generation), we don’t know when the crossovers were formed. There is one generation for each crossover, but until we have Chromosome Mapping we don’t know which generation it is.

Note: A TG Summary Spreadsheet will give good clues to the formation of crossover points – see Observation 5 (see linked blogpost).  In generation after generation the older crossovers can be seen, with only about 2 new crossovers in each generation. So the farther back we go with Chromosome Mapping, the newly formed crossovers will be there (with mother and father on the two sides). But the other crossovers may not appear to be mother/father, unless the origin of the crossover can be determined.

Bottom Line: With TG segments, sometimes the next TG on a chromosome will be the other parent, but more often it will not.

Edit 20240403: It was suggested that I add a Chromosome Map, showing segments from my 16 2xG grandparents. Here is one I did in 2013:

[22CA] Segment-ology: What is the Next Segment? TIDBIT by Jim Bartlett 20231209

A Segment-ology TIDBIT

I was adjudicating a ThruLines from a Common Ancestor (CA) down to a Match. The grandchild of the CA didn’t fit. I find about 5% of my ThruLines are wrong so I just dotted the Match yellow (TL Wrong) to add it to that group. But as I was about to close out the Match, I clicked on Shared Matches (which I usually do anyway). The Match was at 13cM so I didn’t expect much. Surprise – over 20 Shared Matches, and almost every one was confirmed or “likely” to be on the line indicated by ThruLines! A clear consensus. I went back to the Match’s line and found another path that worked – back another generation from the ThruLines CA hint!!

The details don’t matter. The moral of this story is that a ThruLines CA AND a consensus of Shared Matches AND the AncestryDNA “side” should all be in agreement. This applies to CAs at other companies, too – the clues should be in agreement.

Takeaways:

1. When you find a CA, be sure to also review the Shared Matches and the side.

2. When you are searching for a CA with a Match, review the Shared Matches first to see if there is a consensus clue.

PS: this assumes you have diligently done your homework and put all known or likely CAs in the appropriate Notes (same for every company).

[22BZ] Segment-ology: Census TIDBIT by Jim Bartlett 20231206

BLUF: 1. Focus on lower cM Matches in a Cluster to determine the Common Ancestor; 2. Reduce the Cluster upper limit to cull out closer Matches once their ancestral line is imputed to more distant Matches. Known Matches impute to unknown Matches who carry the ancestral line to the next group of Clusters which split only to the parental Ancestors of the previous Matches. Unknown Clusters may well be Bio-Ancestors.

In case you missed one of my many blogposts on Clusters: Clusters form on Ancestors!

This comes from two “facts”: 1. Each of our DNA Matches shares at least one segment of DNA with us that came from a Common Ancestor (CA) – the basic tenant of genealogy DNA testing – the caveat being the segment needs to be Identical By Descent (IBD); i.e. a true segment; and 2. Matches who share the same CA will tend to show up on each other’s Shared Match lists. The inverse is that when a group of Matches show up on each other’s Shared Match lists (i.e. each of your SM lists with them include many of the same Matches), they will almost always share the same CA.

“Clusters form on Ancestors” is a powerful observation – when it happens… And beware the Cinderella slipper – don’t try to force fit a Match into a Cluster if they only share with one or two other Matches – easily seen in SM lists and on the fringes of some Cluster diagrams.

So let’s dive a little deeper. A lot depends on the mix of Matches that are being Clustered. In a perfect world we’d like to Cluster, say, only 3rd cousins (3C) – the resulting 8 Clusters (hopefully) would be 1 Cluster for each Great grandparent. The average for a 3C is 73cM, but a true 3C can range from 7cM to 234cM (per the Shared cM Project 4.0). The point is there is NO cM range that would only include 3C. And it only gets worse with 4C and beyond (and if you follow me – I go way beyond 4C). So: Live with it! We can take some measures to tighten up our Clusters as we Walk The Clusters Back (WTCB).

When we start with an 80 or 90cM lower threshold for a Cluster run, we usually get 4 Clusters, with one for each grandparent. These Clusters tend to follow the rule. But beyond that, with smaller cMs and more distant cousin-Matches, the randomness of atDNA comes into play. We can say the growing numbers of Clusters (as we lower the cM threshold) will tend* to a CA. But I use “tend” because it’s not a guarantee – it cannot be a rock solid rule – “the random DNA didn’t get the memo”.

So, can we have a Cluster using a Cluster run of 60-300cM have 2C, 2C1R, 3C, 3C1R, and 4C Matches in it? Absolutely! They should all be on the same line, but that brings up two important points.

1. Old saying: “Everybody has to be someplace”. The 60-300cM range covers all those cousinships (and more); and in Clustering, every Match “has to be someplace” – it will go into some Cluster! Some of the higher cM Matches (closer cousins) may well have gray-cell links to other Clusters. The way I think about it is that they are “confused” about which Cluster to be in – they are tugged in several directions – but the Cluster algorithm always picks one Cluster. My advice for these Clusters is to focus on the CAs of the smallest cM Matches in each Cluster – usually the most distant Matches – to determine the CA of the Cluster. Hopefully we’ll get a clear consensus (but remember Cinderella’s slipper).  The higher cM Matches in each Cluster often will have gray-cell links to other Clusters – this serves as a QC (Quality Control) check that the several Cluster CAs are related and appropriate. It also confirms these higher cM Matches are closer cousins, descending from all the CAs of gray-cell-linked Clusters.

2. It will also help to reduce the upper cM limit, to cull out some (but probably not all) of the closer cousins as the lower threshold is reduced in the WTCB process. These “closer cousins” have already “done their job” for WTCB. They have helped determine Matches who are one more generation back. In other words, your 2C Matches will help identify your 3C Matches (who have to be from one or the other of the 2C parents). At each Cluster run this information is imputed to the other Matches in their respective Clusters. This is not perfect – there will also be some 2C1R, 3C1R, half 3C, 4C1R in the mix. But it gives you a much better/tighter picture of the CA of each Cluster. These imputed/”tagged” 3C Matches will carry the ancestral thread to the next round of Clusters. Remember, going back in generations, there are only 2 possibilities in the next generation – the father or the mother. Reducing the upper cM threshold will cull out Matches that have already “passed on” their Ancestral line, and will force each new Cluster to group on itself.

The point is to make successive Cluster runs, lowering the thresholds each time to get more Matches, who tend to be a little more distantly related and will divide up into new Clusters which will be a little more distant. In each of these new Clusters there should be a mix of “old” Matches (from previous Clusters, some with known relationships, and some with imputed CAs), and “new” Matches (some with known relationships and CAs, and some unknowns which will be imputed based on analysis of all the Matches in the new Cluster).  

Note 1: Usually, I use CA to note the Common Ancestral Couple between myself and a Match. Clusters tend to form on specific Ancestors. Are they individual Ancestors or the parental couple? I’m not real sure. I will say that I rarely find a Cluster that I can identify solely to a female Ancestor. This makes sense because most of the time the husband/wife couple are together. So I will continue to use the male Ahnentafel number to describe my Cluster CAs.

Note 2: WTCB is a relatively easy process to start, but with each iteration it gets harder – both because of the approximate doubling of Matches at each step but also the inevitably difficult Cluster(s) to sort out (probably a brick wall). In any case you can start manually by just walking down your list of Matches in cM order and coding them (I’d use the Ahnentafel Number) and checking with their respective Shared Match lists. Stop whenever you want. (For me, the first two WTCB iterations were easy (a few hours); and then I worked on one a day for several more…. Your results will vary, depending partly on the amount of “Notes homework” you’ve already done.

Note 3: This is a great tool for bio-Ancestors, Brick Walls, NPEs, etc. Using this WTCB process will identify known Clusters. Some may leave you stumped (a few did for me). One reason you may be stumped is because you have no known/imputed Matches for a new Cluster – just Matches staring back at you with no clue how you are related. The WTCB Cluster comes to a halt. Now’s the time to examine all of the available Trees from the Cluster. If the Cluster Matches have their own CA, you have a BINGO! That’s probably your Ancestor, too. Check any gray-cell links to other Clusters to learn more about where in your Tree this could fit.

[19O] Segment-ology: WTCB Observations and Advice by Jim Bartlett 20231130