Branch Groups

I’m methodically working my way through my Ancestors and Matches using Pro Tools. My main tool is my Common Ancestor Spreadsheet, which is now growing very rapidly. I’m not really in it for the bulk, but for the advantages of Branch Groups. What I call Branch Groups are groups of my DNA Matches under one child or grandchild of one of my Ancestors – these Matches are on the same Tree “branch”.  Such Matches are closer to each other (than to me) and tend to share more DNA with each other. They stand out with DNA shares over 90cM; and I take notice. I can often “fit” them into a Branch Group. On the other hand, I’ve found some Matches that have the right genealogy for a Branch Group, but they don’t share much DNA with others in the Group – more on this below.

Here are some thoughts and observations:

SMOM – Shared Matches of Matches aka “Rabbit Holes” – haha.  When you select a Match and click on the Shared Matches button – you get a list of all the Matches you both have in your respective Match lists. These are your Shared Matches (SMs) with that Match. Each of these SMs shares some DNA with you that you both got from the same Common Ancestor (CA). And, with Pro Tools, you know how much DNA each of these SMs also shares with the “base” Match that *they* got from some CA. Often these two CAs are the same (or one is ancestral to the other); but sometimes the CAs are completely different – *their* CA could be unrelated to you or related to you on a  different line – see Outliers below). When we’ve done our homework and entered Notes for many Matches, we can usually look down the SM list and easily see if there is a consensus, or not – see Birds of a Feather below. Like with auto-Clustering, a consensus indicates a group of Matches that mostly match each other, indicating a Common Ancestor among them. Usually, their CA is also one of your Ancestors – BINGO! This is a Branch Group.  Sometimes their CA is unknown to you – this could be a random happenstance. Or it could be a Floating Branch Group – see below.

Branch Group aka Cluster. When you find SMOMs who share high levels of shared DNA (cMs) with each other they usually form a Branch Group. By “high levels” I mean at least 90cM; but I often drop down to around 50cM as the group grows larger. I consider 20-25cM as “in the noise”, and usually not worth the trip down a rabbit hole. [For your own situation, experiment to find a threshold that usually gives you efficient results.] Sometimes you can get 5-10 (or more) of these SMOMs which link under a child or grandchild or Great grandchild of one of your Ancestors. And then it’s easier to find other SMOMs that fit into the Branch Group. Use an SMOM in a Branch Group to make a new Shared Match list, invariably with new SMOMs… the clues (or rabbit holes) are everywhere! As it turns out in a Branch Group, not all Match descendants will Match all of the other Matches in the group. Remember: at the 4C level, roughly 50% of true 4C won’t show up as matches to each other.

Birds of a Feather.  On many Shared Match lists, a scan of the Notes indicates a clear consensus – most SMs have Notes indicating the same CA; and some are from the same line (up or down a generation). These are birds of a feather – they cluster together. And Pro Tools shows them to be close relatives – these are a Branch Group. In these cases, I’m much more likely to review Matches not yet linked in, and to build their Trees back to find the link. As a quick check, click on a Match and see *their* SMs with you – are they indeed Birds of a Feather? Or not?. For some Shared Match lists, a quick scan of existing Notes may indicate they are all over the place – on both sides; on different branches – so, it’s difficult to determine a consensus. Move on…

Outliers – linked by genealogy, but not linked by shared DNA.  I’ve now run into a very few cases of DNA Matches who are clearly genealogy relatives (in my Common Ancestors spreadsheet) under Ancestor XYZ, but they do not share DNA with other close cousin Matches under XYZ. In each case, so far, they are also related to me in another way, and they do share DNA with their other cousins.  Thinking about multiple segments and/or multiple relationships leads me to Triangulated segments, but I’ll put that discussion off for a future blog post. Just be aware that a Match with one shared segment can only be genetically related one way. Pro Tools may help determine which one.

Collateral SURNAMES in Branch Groups. Less than 1% of my Matches have the same SURNAME as the CA we share [Y and mt lines are pretty rare]. This means my Common Ancestor spreadsheet (tracking the lines of descent down to Matches) includes Collateral SURNAMEs. As I’m working on an MCRA Branch Group in my spreadsheet, I’m reviewing each of my Match cousins, and reviewing all of the  SMOM shared cMs, and checking the Trees of those over 90cM (and glancing at some down to 50cM). Often there is enough to tie those Matches to my Tree (even some with no Trees). It really helps to review the Collateral SURNAMEs already recorded in my spreadsheet for that Branch – that’s usually where I’m going to find a link. And it means I don’t have to build a tree back for each Match – I can usually copy the line of descent of an existing Match in the spreadsheet, and just change the last few generations. A big time saver – in searching and typing… Recognizing a Collateral SURNAME in a Match’s scrawny Tree is helpful. Sometimes I’ll filter a long Shared Match list by a Collateral SURNAME…

Floating Branch Groups. A few times I’ve found a Branch Group that I cannot link to my Tree. They usually include parent/children, siblings, aunt/uncle/niece/nephew, and maybe some 1C or 2C, all in a tight family group. All the interrelationship cMs are on target. But, other than being on a Shared Match list with some known Matches in a Branch Group, I cannot find a link. In most cases this has happened “near” a Brick Wall (or “iffy”) Ancestor of mine. So I’ve created a Floating Branch in my Tree, so I can link other Matches to it. I need to do a study of closest known Matches to see where this Floating Branch is headed – another rabbit hole. Such a Floating Branch could just be a mirage (not really linked to me), or I might find some “tendril” Matches (maybe through a Collateral SURNAME filter) that help find the link. I operate under the belief that ALL Matches over 15cM (and many under 15cM) are true cousins, and many are within a genealogy timeframe and should fit in my Tree somewhere.   

I am now convinced of two things: A) A lot more of our under-20cM Matches are well within our genealogy timeframe than I originally thought; and B) our Brick Walls (out to at least 8C level) have plenty of Matches forming Branch Groups. With each generation going back, it’s harder and harder to figure them out, but Pro Tools can often provide new insights. This helps offset the fact that many Matches have NO Trees or very scrawny Trees. There is hope! But it takes work!

[22CR] Segment-ology: Pro Tools Part 10 Branch Groups by Jim Bartlett 20240812