Can segment patterns help you differentiate matches with paternal grandparent from a maternal grandparent? A tool at DNA Painter helps you do just that. The tool is called Library of Matches – https://dnapainter.com/tools/lom, developed by Cody Ely.
In a blog post titled “Introducing the Library of Matches,” from May 2022, Cody shares how he came up with the tool. He was working on an unknown parentage case and was trying to determine if a 333 cM match was a half-first cousin or a second cousin. He had the idea to look at segment patterns for matches he already knew the relationship for to see if there were any clues in the number and size of segments.
After looking at many known matches, Cody has found that there are segment patterns for grandparents, half-siblings, and aunts/uncles. Cody linked to research done by Andrew Millard (as discussed on Leah Larkin’s blog, the DNA Geek), Kitty Cooper, and the Williams Lab at Cornell University (who have been developing tools and sharing them at HAPI-DNA). These researchers have also found patterns in segment characteristics for specific relationships. Segment pattern analysis, as Cody calls this method of interpreting segment patterns to make predictions, can be a helpful tool in figuring out unknown matches. This could be especially helpful in recent unknown parentage cases.
The Library of Matches tool is a chromosome map with many relationships and the corresponding mapped segments. For example, the Library of Matches includes shared segments for 10 maternal grandparent/grandchild matches, 10 paternal grandparent/grandchild matches, 8 first cousins, 14 first cousins once removed, and 27 second cousins. It also includes many half, removed, and more distant relationships.
Three of my grandparents took DNA tests so I decided to try segment pattern analysis and see if the segments I share with each of them match patterns in the Library of Matches.
Examples from the Library of Matches
This image is from the “Introducing the Library of Matches,” blog post at DNA Painter by Cody Ely. Each row shows a different segment pattern and relationship group. The first row is for paternal grandparent/grandchild matches. The X-chromosome is not used, so these are all autosomal segments.
Source: Cody Ely, Library of Matches tool at DNA Painter, https://dnapainter.com/blog/introducing-the-library-of-matches/, used with permission.
Top row: paternal grandparent examples – long segments, usually 1-2 segments per chromosome, 19-27 (average 23) segments
Middle row: maternal grandparent or paternal half-sibling examples – long and medium with some small segments, 22-43 (average 32) segments
Bottom row: maternal half sibling or aunt/uncle matches (either side) examples – numerous small and medium segments, some long, 35-56 (average 47) segments
Isn’t it interesting to see the patterns?
My Grandparents
To see if these segment patterns are visible with my own matches to my grandparents, I opened up my match list at MyHeritage. First, I compared my shared segments with my paternal grandparents to the findings in the Library of Matches.
Paternal Grandmother
Library of Matches Data Predicts:
- 19-27 (average 23) autosomal segments for paternal grandparents
- usually no more than 2 segments per chromosome
- long segments
Actual Paternal Grandmother Segments:
- 23 autosomal segments
- all chromosomes have 0-2 segments
- most segments are long; with 2 small
Paternal Grandfather
Library of Matches Data Predicts:
- 19-27 (average 23) autosomal segments for paternal grandparents
- usually no more than 2 segments per chromosome
- long segments
Paternal Grandfather Segments:
- 21 autosomal segments
- all chromosomes have 0-2 segments
- most segments are long; 3 are small
Maternal Grandmother
Next, I compared my maternal grandmother’s matches to the findings. As predicted, she shares more segments and there are more medium segments instead of mostly all long segments.
Library of Matches Data Predicts:
- 22-43 (average 32) autosomal segments for maternal grandparents
- long and medium segments with some small segments
Maternal Grandmother Segments:
- 34 autosomal segments
- chromosomes 1, 7, and 12 have 3 segments
- most segments are long or medium; 6 are small
Why do I share longer segments with my paternal grandparents?
Men and women have different recombination rates. The ISOGG wiki states, “Males average about 27 crossovers per child and females average about 41 crossovers per child.” It makes sense that if there are more crossovers when females have children, their grandchildren will share more segments and those segments will be a little smaller.
At Hapi-DNA, the “Paternal and maternal relative detector” tool can be used to detect whether a pair of grandparent/grandchild or half-sibling matches will be related through a male or female parent. I went ahead and tried it using my paternal grandmother’s segments. Pasting in the segments gave me this prediction:
The score was -3.96, so it is strong evidence that the segments are from a paternal grandparent. At first I was confused about the score being negative, but then I realized that the higher negative scores are paternal, and the higher positive scores are maternal. But a score between 0-2, whether positive or negative, is in the overlap range, making it less certain.
I tried again with my paternal grandfather’s segment and got this result:
Lastly, I used the segments I share with my maternal grandmother.
Both the Library of Matches and HAPI-DNA tools correctly predicted whether the grandparent match was maternal or paternal each time. This is neat!
Try the Library of Matches and HAPI-DNA tools
The free tool, Library of Matches, developed by Cody Ely, is available at DNA Painter. Give it a try here: https://dnapainter.com/tools/lom. For ideas about how to use it, see “Introducing the Library of Matches,” blog post at DNA Painter by Cody Ely.
I also recommend the tools at HAPI-DNA! Find them here: https://hapi-dna.org/
1 Comment
Leave your reply.