Chromosome Mapping – A First Pass

I’ve seen some of the wonderful chromosome mapping images that others have generated (displaying which segments of their DNA they have traced to particular ancestors), but I hadn’t yet gotten around to mapping any of my own DNA. Letting the perfect being the enemy of the good, I figured I hadn’t done enough analysis to be ready to map my own data.

Earlier this week, I watched Blaine Bettinger’s webinar, Reconstructing Your Genetic Family Tree, and he walked through how to use DNA Painter to build a chromosome map with segment data shared with DNA matches (from 23andMe, FamilyTreeDNA, MyHeritage, and/or GEDmatch). (I do use other tools at the DNA Painter website regularly, and find their Shared cM Tool and What Are The Odds? very useful.)

The whole webinar was a nice overview of the process and its benefits, but a few key takeaways helped me get started with my own map:

  • A map can be a work in progress; adding more data can help you correct errors as you go.
  • One of the best types of matches to use can be second cousins (they share a lot of DNA with you that should be specific to your great-grandparents).
  • Even if you have multiple family members DNA tested, start mapping your own chromosomes first.

Luckily, I have three known second cousin matches. I also have three matches who are first cousin to one of my parents (even more DNA shared). (There are even more through AncestryDNA, but alas, Ancestry has no segment data available for matches.) So, after a first pass, here is my resulting chromosome map. 

DNA Painter Chromosome Map for myself, using matching segment data from one of my father’s first cousins, one paternal second cousin, two of my mother’s first cousins, and two maternal second cousins. The default cutoff of 7 cM was used to filter out small segments.

Approximately 24% painted, it’s far from complete (even at just the great-grandparent level), but it’s a start. I have representation from three out of my four pairs of great-grandparents:

  • Benjamin Franklin “Frank B.” Wright (born in Delaware) and Mabel Laura (Hulbert) Wright (born in New Jersey)
  • John Joseph Fitzpatrick and Margaret Mary (Hearne) Fitzpatrick (both born in Ireland)
  • Alfred Gerald Mooney (born in Ireland) and Helen “Ella” (Rutledge) Mooney (born in Pennsylvania)  

In the webinar, Blaine Bettinger also pointed out that the results of visual phasing can help fill in parts of your chromosome map. I’m lucky enough to have DNA test results for my mom, three of her siblings, and two of their first cousins, making visual phasing possible. I have started, but not yet finished phasing their DNA; hopefully once I make more progress with that, I can fill out even more of my map. And then there’s all those more distant cousin matches…

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