Shared Centimorgan Project Updates: Why You Should Care

Diahan Southard

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The Shared Centimorgan Project (ScP) has exciting and important new updates. Here’s why they matter to your DNA match experience and how to submit your own data.

In any industry, you can often pinpoint distinct innovations to the way we work. They can range from a simple cog in a large wheel that may increase efficiency or accuracy, to major machines that replace manual labor.

In the genetic genealogy industry, one of those major innovations is the Shared Centimorgan Project (ScP). Launched in 2015 by my dear friend Blaine Bettinger, the ScP is a crowd-sourced tool to help us determine how much DNA is actually shared by individuals with specific relationships. Everyday genetic genealogists reported to Blaine the amount of DNA we saw shared between individuals with specific, known relationships. He collected and analyzed all that data and created a table that showed the average amount of shared DNA as well as the range of values that were found.

The ScP tool has been invaluable. I have used it every day since it came out.

But it did have limitations. Conclusions about the amount of shared DNA to expect for specific relationships could only be as good as the data. For some categories, there just weren’t very many submissions, so we just had to do the best we could.

Updates to Shared Centimorgan Project

But on March 27, ScP 4.0 was released with a 147% increase in data!! Now, I love data. Data tell so many interesting stories. Data gives us power to make decisions and draw conclusions. So I strongly encourage you to read the full PDF release about the project.

If you don’t have time or inclination to read all 56 pages, here are some of my favorite takeaways:

  • There are now a total of 55,418 data submissions (we still need more–submit yours HERE).
  • The lowest number of submissions among the 48 different relationships analyzed was 33 submissions for 5C3R, but 5,281 of us reported 2C1R.
  • The ranges were calculated after removing outliers as well as 1% of the data (taking 0.5% from the high and low ends of the spectrum).
  • HISTOGRAMS! These are so valuable, and are now included in the interactive version on the DNA Painter website.
  • The line chart on page 21 shows how relationships between Half 1C3R and 4C1R (of which the project lists a total of 15 separate relationships) have so much overlap that it is very, very difficult to tell your relationship by only looking at the DNA.

The histograms on pages 48-51 showing multiple relationships overlaid on top of each other is EXTREMELY interesting. For example, the full/sibling half sibling chart shows us some pretty revealing information about the genetic line between full and half siblings, and what it means to be on either side of it. My other favorite is the 1C/Half 1C chart that shows there is certainly a “danger zone” where both relationships are equally likely and therefore nearly impossible to genetically distinguish.

The More You Know, the Better

As I said, data is power. The more you know about those numbers that connect you to the cousins on your match list, the better able you are to make decisions about where and who to research next. Because, no matter what, you will always have to DO GENEALOGY to fully determine your relationship to others.

Find out what else your DNA can tell you with our free guide, 3 Things DNA Can Tell You About Your Birth Roots.

Take me to that free download!

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<a href="" target="_self">Diahan Southard</a>

Diahan Southard

As founder and CEO of Your DNA Guide, Diahan Southard has been teaching people how to find family history answers in their DNA for several years, and she's been in the genetic genealogy field since its infancy. Diahan teaches internationally, writes for popular magazines, consults with leading testing companies, is author of Your DNA Guide–The Book, and producer of Your DNA Guide–the Academy, an online learning experience.


  1. Barbara Raemer

    on my paternal side I have a 2C1R that is a double cousin. 2 McGinnis brothers (my grandfather, her ggrandfather, married 2 Cary sisters. Does this make endogomy an issue? just for our common matches? on the WV/KY Cary line there could be other situations, but not to my knowledge.

    • Diahan

      Endogamy is marrying within a group over and over. This is just multiple relationships. So you are double 2C1R. So your common matches will contain people related to both of these ancestral lines.


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