The Shared cM Project: Tracking individual contributions

Do you know about Blaine Bettinger’s Shared cM Project?  It’s the crowd-sourced collection of shared centiMorgans (cMs) for the purpose of analyzing the ranges of cMs found at different levels of relationship (full siblings, half 1st cousins, 2nd cousins, etc.)

If you and your known relatives have done your DNA tests at any of the big vendors, you can submit your data here.  Relationship is asked for, but no identifying information (except your email) is needed for submission.

I have been submitting my own DNA data since 2016 — Blaine released the first results in May 2015.   However, so that I won’t skew the results (with duplicate or triplicate submissions), I keep track of my submissions in my own Excel spreadsheet.  A sample of the page I use is below, filtered on just some of the 2C1R relationships I have submitted.  (I have hidden the names of the two testers involved in each relationship.)

Submission_Shared cM Project

Note that the cM range for my submissions of 2nd cousin 1 removed is from 32 cM to 267 cM.  The vast majority of relatives at this level were known beforehand, or otherwise targeted tests.  In the case of the tester who only shares 32 cM, they share that cM with one of 1st cousins.  The rest of us — my siblings and I — and my 1st cousin’s siblings share a much more “typical” amount of DNA with the tester, around 110 – 140 cM.  And since we all match at the full-sibling level, and at the full 1st cousin level, it (so far!) appears that the 32 cM is just due to the randomness of DNA inheritance.

One thing I did in the beginning was submit a relationship for each vendor.  (My father, for example, has tested at 23andMe, FTDNA, and Ancestry, as have I.)  So, originally, I submitted 3 different sets of father/daughter data.  (Obviously, the cM count varied in only minor amounts.)

Since mid-2017, though, I only submit once no matter how many places the two testers have tested at.  (Blaine does ask for the vendor name when you submit.)

In general, I have said no endogamy — but that is based on what I know of the relationship.  Who knows?  With enough research on certain lines, I may find that indeed there was endogamy.

I also, for my own interest, track “expected” DNA shared with actual DNA shared (assuming grandparents and uncles/aunts share an average of 25% with the tester, first cousins share an average of 12.5%, 1st cousins removed (1C1R) 6.25% and 2nd cousins 3.13%.)  It never fails to amaze me how my sister, brother and I have such variations in the amount of cM shared with a given targeted cousin.

How do you track your submissions, if you are submitting to the Shared cM Project?  Are you concerned with not submitting twice — or do you figure it will all average out in the end (certainly a possibility)?

Cite/link to this post: Cathy M. Dempsey, “The Shared cM Project: Tracking individual contributions” Genes and Roots, posted 31 Mar 2019 ( : accessed (date)).


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