The Shared cM Project is an important and powerful tool for genetic genealogy – particularly with it’s integration with the DNA Painter tools. Over 60,000 submissions is impressive.

Two observations on the Shared cM Project – a very high percentage of the submissions were for the closer relationships; and the data was from many different users (perhaps with varying degrees of accuracy).

I now have over 9,000 entries in my Common Ancestors spreadsheet [see my  blogpost about this spreadsheet tool]. I’ve curated these down to 7,800 entries from 1C to 8C, that I am pretty confident are correct. Also, my analysis is that there is a high probability, based on Trees and Shared Match Clusters, that each shared segment is from the Common Ancestor.

So I decided to compile cM statistics from my own curated data. I also wanted to see how the small cM relationships played out.

My data is not nearly as robust as the Shared cM Project was for 4C and closer relationships. However, in the 5C range my data was closer; and in the 6C to 8C range I generally had more data points than the Shared cM Project. This reflects my emphasis on all Ancestors out to 8C range.

Overall, there were no big surprises. In general, for 6C to 8C my data was in a tighter range; and I had some data for distant relationship that weren’t in the Shared cM Project (but, no surprises)

Bottom Line: In my opinion the ranges in the Shared cM Project are a little broad – probably a reflection of data from so many sources. I think the broader ranges give folks more wiggle room with low percentage probabilities, when they should really be looking for other possibilities.

Here is my table comparing my data with the Shared cM Project data – the top row indicates the full cousinship; once removed (1R) and twice removed (2R):

The significant increase in data points at the 6C level reflects the power of ThruLines to build Trees back (subject to my review); but only out to 6C.

As always, feedback is welcomed.

[06F] Segment-ology: Shared cMs for Small Segments; by Jim Bartlett 20420605

A Segment-ology TIDBIT

Up Front – it’s the one with the highest average cM among Match cousins.

Setup: You’ve pretty much determined a particular couple are bio-Ancestors to youself (or someone else) – often by a consensus of Match Trees in a group (usually a Cluster) – see here. However, this bio-couple had a number of children. Which one of them was the bio-Ancestor? It gets harder and harder the more generations back you are researching.

Process: I’ve had good outcomes by determining as many DNA Match cousins as possible for the bio-Ancestor couple. Line up the DNA Matches and the shared DNA cMs under each of the children, and then determine the average cM for each child. In general, one of the averages will be somewhat more than the others – even when you don’t know the link. That’s because you are a closer cousin with Matches who descend from the same child as you do.  For instance, you may be a 5C through most of the children – sharing an average of 25cM with those Matches; and you would be 4C with the Matches who descend from then one child who is your Ancestor – sharing an average of 35cM with them. Of course, our results may vary somewhat from the Shared cM Project, but it’s the concept we are focused on here.

When I do this analysis, I drop down into the smaller segments, in order to get a fair comparison among all the cousins I can find. The more Matches we use, the more it averages out to the Shared cM Project and the correct bio-Ancestor child.

[22CI] Segment-ology: Which Sibling Is the Bio-Ancestor? TIDBIT by Jim Bartlett 20240403

Free eBook: Genetic Genealogy: The First 25 Years – 82 pages – the reflections of 34 Contributors – compiled and edited by Diahan Southard. This is a fascinating read from cover to cover. And it’s free to download here: https://diy.yourdnaguide.com/so-far

I am honored and humbled to be included in this project. And a grateful hat-tip to Diahan who conceived this project; herded the cats to gather the various perspectives; curated and edited the inputs and got it ready before RootsTech 2024. And made it free to everyone!

Thanks, Diahan Southard.

[99C] Segment-ology: Celebrating the First 25 years of Genetic Genealogy by Jim Bartlett 20240229

A Segment-ology TIDBIT

My previous post noted that ThruLines quickly adapted when I changed my Tree.

Setup: I have looked at every one of my ThruLines Matches. If you are not sure, just open your DNA Matches list and select the Filters: Unviewed AND Common Ancestors. If you’ve looked at them all (and hopefully added appropriate information in the Notes box for each one), after a minute or two you’ll get a message: No matches match the selected filter. You’re now ready to take advantage of this status.  

I have a pesky female Ancestor. I’m not really positive where she fits in a larger part of my Tree (or to any of several floating branches).  So I called up her profile; clicked on Edit (top right); clicked on Edit relationships; and clicked on the parent “X”s (to separate, not delete, them). I now went to the Father box and clicked on Add father; and typed in a name I wanted to test as a parent. I then closed the Edit relationships page and went back to my DNA Matches List and filtered on Unviewed AND Common Ancestors…. and ThruLines immediately populated appropriate new Matches who would be cousins through that parent. In the one to two minutes it takes ThruLines to search my 93,000 Matches, it found and listed Matches with ThruLines. Since I had already opened all previously known ThruLines, this new listing was only Matches who were related through the change I had just made. I quickly took notes and reset the original pesky Ancestor. Ready for the next trial. In and out very quickly.

There is more to this story for a later blogpost. The point for this blogpost is twofold:

1. AncestryDNA must already have most of these relationships already worked out, just waiting for me to ask the right question (do you have cousins for “this” relationship?)

2. There is no waiting days for a “refresh” – ThruLines reports as fast as it can scan my Match list (down to 6cM). Just WOW!

Both of these are pretty amazing, IMO.

[22CH] Segment-ology: Thru-Lines is Quick – Really Quick!! TIDBIT by Jim Bartlett 20240228

A Segment-ology TIDBIT

I was entering a ThruLines line of descent into my Common Ancestor Spreadsheet, when I noted an error in the Match’s Tree. The Tree and ThruLines were at 6C. When I inserted the missing generation in my Tree, the relationship changed to 6C1R. As soon as I clicked back to the Match, the ThruLines was gone!  AncestryDNA now *knows* the correct relationship, and since it was beyond 7 generations for one of us, they won’t show it.

Heads up. Copy or screen-shot before you lose the ThruLines link. I guess in a pinch, I could go back to my tree, take out the generation I added, and ”reincarnate” the ThruLines link. Sometimes you have to think like a computer…

[22CG] Segment-ology: ThruLines is Quick! TIDBIT by Jim Bartlett 20240225

As I look at ThruLines Matches under 15cM, roughly half of them have a Side (Maternal or Paternal) which is different from the Side of the Common Ancestor proposed. What’s up?

AncestryDNA has determined a “side” (Maternal or Paternal) for most of my Matches. Pretty slick! And very helpful!! For above-20cM Matches they appear to be fairly accurate. This is despite the fact that all of my Paternal and half my Maternal Ancestor were mostly from Colonial Virginia. I was expecting a lot of Matches to be “Both”, but relatively few are. The bulk of my Matches are in the Maternal and Paternal categories. And below 15cM, the Maternal or Paternal “sides” are not aligning with the “side” for many of the ThruLines Common Ancestors. Side note: it appears that Ancestry is now only reporting one ThruLines Common Ancestor per Match – they used to report two or three if they found them….

What are the possibilities?

1. The AncestryDNA “sides” may be incorrect. I’d like to think (hope?) that the science behind them is valid and that they are largely correct. Most of mine above 20cM appear to be.

2. The ThruLines may be incorrect. This is a genealogy area (not DNA). With my 50 years of genealogy research, I already know many of the descendants of my Ancestors, and I run a check (not-GPS-comprehensive) on each ThruLines reported. I used to spot about 5% with errors (some of which were easily fixed), but now there are more and more as AncestryDNA appears to have become fairly aggressive at finding Common Ancestors. It appears they have loosened up the algorithms to allow “close” name variants and “close” dates, resulting in more false results. But even with the ThruLines I review and accept the Common Ancestor from a genealogy point of view, there are roughly half which don’t agree with the “side”.

We cannot have it both ways… or can we?

When AncestryDNA determines a Maternal “side”, does that guarantee that 100% of the Match’s atDNA can only be on my Maternal side? I really think that is absurd! Particularly when you consider most of my Ancestry is from Colonial Virginia. Surely my Colonial Virginia Matches could descend from Ancestors who would be on both sides of my Ancestry. In fact, I have several of my own Ancestors who, due to distant pedigree collapse, are on both sides of my Tree.

I think it is entirely possible that the bulk of a Match’s atDNA could align with my Paternal or Maternal DNA, but that some of the Match’s segments could be from the other side. I’m scratching my head over whether or not this could occur half of the time.

3. Both Ways! My conclusion is that we can have it both ways! I have a colored Dot for cases with both “sides”, but I’ve decided not to let that, by itself, stand in the way of accepting a ThruLines Common Ancestor as valid.

I’m curious about your overall experience and observations about conflicting “sides”. You are encouraged to add your insights in the comments.

[35AA] Segment-ology: AncestryDNA Side vs ThruLines Side by Jim Bartlett 20240213

A Segmentology TIDBIT

Ancestry’s ThruLines is like “dumpster diving”… sometimes you have to dig through the trash to find the pearls. Sometimes there is a smorgasbord of various genealogy junk, but sometimes there is a treasure trove of good information. Pick and choose wisely…

[22CF] Segment-ology: ThruLines Levity TIDBIT by Jim Bartlett 20240211

A Segment-ology TIDBIT

Thinking about Small Segments and Distant Matches…

Many have used the Speed and Balding IBD Statistics in Figure 2 of their Paper …  This chart has often been used to scare us away from small segments [by small I mean 7-to-15cM Shared DNA Segments – I do not encourage anyone to use smaller/”tiny” segments].

The vast majority of our Matches at AncestryDNA fall into this 7-to-15cM category, and I get many ThruLines Matches which have valid paper genealogies. They may not all link to the DNA, but I see no reason to discount them based on the small size of the Shared DNA alone. ThruLines is limited to Matches who are related as 6C or closer – not what I would call a “distant” Match. Only the small Shared Segments and the constant reference to the Speed and Balding chart, warning that small segments are usually distant, stand in the way.

This got me to thinking (watch out!)… The AncestryDNA Timber algorithm is well known to “down weight” the cM of many of our Shared DNA segments. Click on the “DNA” line in any Match Profile to see the “Unweighted share DNA” amount – often somewhat larger than the amount shown on the DNA Profile. This is Timber at work, downweighting the DNA that would be shown at, say, GEDmatch. One of the effects of this downweighting is that many of the AncestryDNA customers who would show up as a Match at GEDmatch are never shown as a Match to us at AncestryDNA!  It seems to me that AncestryDNA has already compensated for the statistics reported by Speed and Balding. It is thus unfair to compare our Match lists with the Speed and Balding statistics.

I’m not saying that some of our Matches are not distant – some of them are. What I am saying is to let the chips fall where they may. If we can find a Common Ancestor – at *any* Shared cM amount – why not accept it (if it also passes a genealogy review). The Shared cM Project clearly shows small Shared DNA Segments in the range for cousinships at 3C and more distant. Why should we be frighted away when our Match falls into the small segment category?

My blog post about a Common Ancestor Spreadsheet (here), now has over 8,000 rows of Matches with Common Ancestors with me. I sort them to get “nested” family groups, and draw comfort as I see the closer families and note they are Shared Matches with each other. New ThruLines have been pouring in recently (and the quality is dropping off a little). As expected in my Common Ancestor spreadsheet, a majority are in the small segment range. I am not worried about the cM size as long as the genealogy is valid!  

Bottom line: Let the chips (small Shared cMs) fall where they may; and focus on the genealogy.

Happy New Year!

[22CE] Segment-ology: Let the Chips Fall Where They May TIDBIT by Jim Bartlett 20240101

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