I previously talked about chromosome painting (1) and how you can paint DNA matches you know to assign your DNA to your ancestors. Let’s review the basics of recombination before we jump to talking about inferred chromosome painting. My mom has two chromosomes, one from her mom and one from her dad, and those two chromosomes got mixed up (recombined) and one of those mixed up chromosomes was the single chromosome that I got from her. This chromosome could have contained all the DNA from her mom (if it recombined with another chromosome from her mom) or all the DNA from her dad (if it recombined with another chromosome from her dad), but more likely it had a mix of DNA (the chromosome from her mom recombined with the chromosome from her dad) as represented here. So the blue pieces in my chromosome came from grandad, and the yellow piece came from grandma.

Remember this guy? He provides a catch-phrase for inferred matching. He calls his parents “Mama” and “Not-the-mama.” Similarly, I can refer to the blue parts of this chromosome as “Not-grandma” and the yellow part as “Not-grandad.”

The problem with our chromosomes is that they don’t come labelled as “grandma/not-grandad” or “grandad/not-grandma.” We have to use our DNA matches to fill in the blanks. For example, I have a match with known cousin D. D and I share a common ancestor through my maternal grandfather. I can confidently label those painted segments of DNA as “grandad” like this segment on chromosome 1 pictured below. Any match that is on my maternal side and matches me in the same place as D will be from the branch of my tree that I share with D. For example, if i didn’t know who H was, I would at least know that our common ancestor is on the line I share with D.

More than likely, my mom is going to share more DNA with D than I do. This is because she doesn’t have to choose between having her Mom and Dad’s DNA; she has both. But when recombination happened, and I inherited a single chromosome, I got one or the other, which means that I didn’t get some of those segments my Mom shares with D, like here on chromosome 9:

However, all is not lost! Just because I can’t paint that segment as grandad, I can still learn something from knowing that the segment I got is “not-grandad,” because another way to write “not-grandad” is “grandma.” Therefore, I can paint the segment data that my mom shares with D on my own chromosome painting. I will name the match “D -inferred” so I don’t get confused with the spots where I do match with D. I will give the match the same colour I use for my maternal grandmother’s parents. When I paint it I can see my inference was correct, because it overlaps with where I match with R, a known match on my maternal grandmother’s side.

If I didn’t have a parent to compare with, I could also do inferred matching with any of my siblings, because they will likely will have inherited segments than I didn’t. So my sibling might share segments with D that I do not, and the same “grandad” “not-grandad” logic applies. Half-siblings will also work, as well as the descendants of your siblings, but using other close relatives as your reference has to be done with caution.

If you want to read more about inferred matching, I highly recommend Jonny Perl’s blog posts on it, which you can find here (9) and here (10). In the second post he links to a very good webinar (subscription required) (11) by Blaine Bettinger, who calls it “Deductive Chromosome Mapping.” Happy painting!

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1) Jennifer Wiebe, “Chromosome Painting,” Jennealogie (https://maltsoda.wordpress.com/2022/04/14/chromosome-painting/ : accessed 16 April 2022).

2) Jennifer Wiebe, digital photo, Recombination, April 2022, author’s files.

3) “NOT THE MAMA!” Dinosaurs TV SHOW Facebook Group (https://www.facebook.com/378455545842408/photos/not-the-mama/378458525842110/: accessed 16 April 2022).

4) Jennifer Wiebe, digital photo, Shared DNA with D on FTDNA, April 2022, author’s files.

5) Jennifer Wiebe, digital photo, Painted Chromosome 1, April 2022, author’s files.

6) Jennifer Wiebe, digital photo, Mom’s shared DNA with D on FTDNA, April 2022, author’s files.

7) Jennifer Wiebe, digital photo, No shared DNA between me and D (FTDNA), April 2022, author’s files.

8) Jennifer Wiebe, digital photo, Painted Chromosome 9, April 2022, author’s files.

9) Jonny Perl, “Painting your DNA with inferred matches,” DNA Painter (https://blog.dnapainter.com/blog/painting-your-dna-with-inferred-matches/ : accessed 16 April 2022).

10) Jonny Perl, “More tips for inferred chromosome mapping,” DNA Painter (https://blog.dnapainter.com/blog/more-tips-for-inferred-chromosome-mapping/ : accessed 16 April 2022).

11) Blaine Bettinger, “Advanced DNA Techniques: Deductive Chromosome Mapping,” FamilyTree Webinars (https://familytreewebinars.com/webinar/advanced-dna-techniques-deductive-chromosome-mapping/ : accessed 16 April 2022).