Mapping a DNA Match in a Chromosome Map

In this demo, you can learn the mechanics of mapping a DNA match in a chromosome map at DNA Painter, as well as the thought process that can help you to narrow down the ancestral source of each segment and draw conclusions from that match.

[@mamabear52]

Thank you, that helped

[@billdillon8139]

Thank you. You make it look so easy.

[@PascalEricSacrepay]

Hi , thank you for sharing this, I have one question that maybe others thinking of, what it mean when a group of dna matches share let say only one segment, but for some it start at the same location, but for others it end at the same location, any insight?

[@dna.painter]

Hi
Thanks for your comment.
Before I dive in, bear in mind that the start and end positions are 'fuzzy' and not precise, since the matching is based not on whole genome tests, but on SNP tests where a selection of SNPs are tested.
When you share a segment with a match (assuming it's a genuine segment and not an error in the matching algorithm), it's because the ancestral segment you inherited from an ancestor overlaps with the ancestral segment that your match inherited from them. These ancestral segment are created whenever you and your ancestors had a crossover, switching between inheriting DNA from the two grandparents on that side.
The most likely explanation for the phenomenon you describe is that you or one of your direct ancestors had a crossover at the start and/or end position. Some matches have an overlapping ancestral segment that is bounded by a crossover (on their side or yours) at the end, while others have one that is bounded by a crossover on the left.
You might find my recent webinar on Practical Chromosome Mapping at Legacy Famliy Webinars useful: familytreewebinars.com/webinar/practical-chromosome-mapping-gaining-insights-from-segments-of-dna/
Thanks

[@Disblair]

Great video in which you make this process look incredibly simple. Unfortunately I think it would be too complicated for me 😢. Perhaps AI will be able to do this in the future 😮. I guess I’ll be pushing up the daisies by the time, if any, Ancestry allows this 😢.

[@dna.painter]

Thanks. If you're able to try it, you might find it's easier than you think! To get segment data you would need to transfer your DNA to another site such as FamilyTreeDNA, MyHeritage or Gedmatch.

[@CarolAnn61]

thank you for making it simple :)

[@billdillon8139]

But if your parents died without having their DNA tested, and you're an only child, then you are severely limited in this technique. I strongly believe that my paternal grandmother was either (1) adopted or (2) the result of an NPE. And that is a brick wall for me. I have a 1/2 aunt that we believe has my grandmother as her mother. We have 1089 cM of sharec DNA. Suggestion?

[@dna.painter]

Hi Bill. In fact in the example in this video, my father in law's parents are also deceased and he does not have any tested siblings, so what would stop you being able to do this for your brick wall line would be the lack of genealogical info rather than having deceased parents and being an only child.
To work out what's going on with the 1089cM match, you would scrutinize the shared matches - people who match both you and this person, and try to fit them together in a genealogical tree. If you're able to do this, you could try the What Are the Odds tool at DNA Painter to test out your hypothesis and consider others. 1089cM is certainly consistent with a half-aunt but there are a few other possibilities that it would be good to eliminate: dnapainter.com/tools/sharedcmv4/1089

[@rotagbhd]

Neither parent being tested, and being an only child should not have much limitation to this technique. This technique should help identify your unknown ancestors. Names are arbitrary, they are just identification labels after all. If your grandmother is adopted, you could label her parents as "1GGF SURNAME-A" & "1GGM SURNAME-B". Their parents could be, "2GGF SURNAME-A" + "2GGM SURNAME-C", and "2GGF SURNAME-B" + "GGM SURNAME-D", or whatever naming method makes sense to you, it's arbitrary.
As you map your matches to these people/labels, no matter their name, it will still tell you from whom each segment of DNA comes from. And with some luck and research, through triangulation you could potentially identify these people from your match's trees. If you have multiple matches that share some segment of DNA to your unknown ancestors, maybe your matches have the identity of that person in their tree, and this technique will prove that is your ancestor as it is their DNA after all.
I would make a crude spare tree and fill it in based on the info of my matches' trees and the probability of relations based on cM shared. Go to DNA painter's shared cM chart, enter the cM, and it will tell you, X% chance this person Grandparent, Y% Chance this person is a 2nd cousin, etc.