A Segment-ology TIDBIT
To paraphrase Lewis Carroll: If you don’t have an objective, any path will take you there.
I sometimes think about this with respect to genetic genealogy. Over 30 million people have taken a DNA test – there are probably many objectives, whether stated or not.
Over the past few years our community has developed a range of tools; and folks ask: “Which tool should I use? Which one is best for me?” Well… it depends. It depends on your objective(s).
You may have several objectives… I’m asking you to write one down. Edit your objective statement until it’s clear and concise. Make a simple sentence. Then we can think about the tools… which ones will help you achieve your objective.
Let’s look at some examples of objectives and the tools we might use. NB: These are *my opinions*.
1. Determine my ethnicity (aka admixture, heritage, geographic mix, etc) percentages. You only need reading skills for this one. Take a test and read the results.
2. Find my close cousins who have done DNA testing. Test at AncestryDNA and build a Tree of your Ancestors there. Then look at the ThruLines program for Matches who share a Common Ancestor with you (back as far as 7 generations). Also test at the other three major companies – you never know where a close cousin might test. For extra credit: verify their line of descent; contact them and share information.
3. Determine a bio-parent. Let your Matches provide a pointer. At AncestryDNA, list your top Matches with Trees; list their ancestors; analyze these lists to find 4 families; build the families down and find two intermarriages – who are probably the grandparents. Sometimes it’s as easy as it looks, sometimes the answer is elusive. The point is: for this objective you often don’t need any of the Clustering or Triangulation tools. Your objective is very close, and your close Matches often have the information you need.
4. Organize (group) my Matches on my Ancestors. Use Shared Match Clustering and/or DNA Segment Triangulation methods. Both of these methods work very well. It’s still up to you to determine the Common Ancestor within each group. The point is: These methods group your Matches on Ancestors.
5. Determine which segments came from which Ancestors. This is Chromosome Mapping. We need DNA segment Triangulation to map the DNA – a lot of grouping work using data from GEDmatch, MyHeritage, 23andMe and FamilyTreeDNA. We need to determine a lot of Common Ancestors with a wide range of Match cousins – a lot of genealogy work (best done, IMO, at AncestryDNA – and often involving extending Matches’ Trees). We need to build the evidence for each ancestral line & segment combination. The point is: Several tools are needed – and it’s a major project.
Recommendation: Write down an objective statement. Then select the tools that will get you to your objective most effectively. For most of us, genetic genealogy is a hobby – so use whatever tools work best for you, and have fun.
[22BG] Segment-ology: What Is Your Objective? TIDBIT by Jim Bartlett 20220508
segment-ology 
If my bio father’s grandson by another half brother took the Ancestry.com DNA test and I took the same DNA test would that be enough to establish that this bio father is indeed my father?
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Mark – No, not by itself. It would certainly give you another data point. Except for parent/child relationships, a single DNA Match is usually not the only evidence needed. But it could be a very significant piece of evidence.
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In this scenario, the grandson is your half-nephew. According to the Shared cM Project, a half-nephew should share an average of 871 cM with you, but anything in the range 492-1315 is possible. If the amount of shared DNA with your half-nephew falls outside this range, you might consider alternative explanations about the familial connections. Consultation with an expert genetic genealogist is suggested.
Data Source: The Shared cM Project 4.0 tool v4 (https://dnapainter.com/tools/sharedcmv4).
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Andy – You are a Segment-ologist now! And you are right, as you finish off the low hanging fruit, it does get harder. But on the other hand, you have a wider, deeper base, which I find very helpful. A TIP: At GEDmatch 0ne2Many – sort the list by total cM and company – then start at the top of Ancestry part of the list. The high cM Matches are somewhat easier to find at Ancestry – this gives you TGs for some Ancestry Matches… Jim
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Jim, I have done and am continuing to do your recommendations #2, #3, #4. What has consumed most of my time recently is #5, chromosome mapping. After organizing all my matches >15 cM using an Excel spreadsheet, I switched to using GDAT. Initially, I had tried to use GDAT but found it intimidating. In the process of creating the Excel spreadsheet, I became more knowledgeable, which better prepared me to use GDAT. I like how GDAT keeps all the information organized in one place. Many of my hints have come from Theory of Family Relativity at MyHeritage. Currently, I’ve mapped over 100 segments to 15 different MRCA couples in the range of 3C-5C. Of course, some of the segments are overlapping so there is maybe 30% coverage of my paternal chromosomes and just a little bit of the maternal because she was born in Germany. An exception is a strong match on someone who also traced back to an MRCA pair who lived in a small town near Magdeburg, Germany in the mid-1700’s. What’s great about chromosome mapping is that it’s helped to push back the “frontiers” of my family tree, while at the same time confirming paper trail lineages. However, I am running out of low-hanging fruit, and the going will undoubtedly start to get harder. Chromosome mapping is, as you said, very time-consuming, yet it is quite amazing to see the pieces fall into place, using them to predict where other matches in the same triangulation groups are located in the family tree.
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Great Objective. And you are correct – once you’ve mapped all of your DNA, each new Match is relatively easy to add to one overlapping TG or the other. And each TG turns into a Micro project, focused on one Ancestral line. I hope you’ll report back when you reach this Objective – it’ll be time to work on the next Objective;>j Jim
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Jim, I keep thinking of your presentation at ECGGC on how you mapped 100% of your genome. That is my goal at present, to equal your achievement. Perhaps you work at the Micro level with individual triangulation groups. The Macro end is the reconstruction work that Kevin Borland is developing. I hope to pursue both approaches. Once I have my whole genome organized, I would expect to be able to make a pretty good prediction on each new DNA match I examine.
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