Many families have grandparents or great grandparents who are first or second cousins. Within family marriages did not used to be as unusual as they are today. However for those of us who work with DNA, the extra relatedness adds confusion to interpreting the comparisons of their descendants. Plus there are people whose parents are related. It would be nice to have some charts showing the expected DNA amounts in these more unusual relationships.
Some of you are familiar with the statistics Blaine Bettinger has collected for more ordinary relationships. (Click here to contribute your numbers there) The calculator at DNApainter, which we all use to check the possibilites for an unknown DNA relationship, is based on his research and the statistical work of Andrew Millard and Leah Larkin.
Now Blaine is collecting the data for these more unusual relationships. So any of you who have DNA results from known double cousins or other family members whose descriptions fit, please click that image below to go to the form where you can add your numbers to his new project.
There are more places to contribute your numbers
This is the last call for you to contribute your X chromosome statistics to my survey. Click here for my post explaining the project.
This is the fifth year of the survey of best genealogists in a number of categories conducted by Canadian genealogist John D Reid at his blog Canada’s Anglo-Celtic Connections. Please vote for your favorites.
This is the second DNA only conference by I4GG.org so don’t miss it. It will be in my hometown, San Diego, the weekend of October 22-23. The weather will be lovely, as always, and I will be doing a session on the tools at GEDmatch.
And my final reminder, please contribute your DNA statistics to my study on the differences between half siblings matches versus aunt/uncle/niece/nephew matches versus grandparent /grandchild matches. This is particularly important for helping adoptees. The hope is that when they get one of these matches, maybe it would be possible to tell which relationship it is without testing more family members. Click here for my post on that.
The question I often see is are we really 2nd or 3rd or 4th cousins? The answer is usually “maybe.” A 2nd-4th cousin designation by your testing company is purposefully vague. Best to look at the amount of shared cMs in segments greater than 7cM, number of segments, and the sizes of those segments; plus, of course, who else this new DNA relative matches!
DNA inheritance gets more and more random the further away the relationship is. The amount of DNA you share with someone more distant than a 3rd cousin is impossible to predict and even those 2nd and 3rd cousins seem highly variable. So the statistical study conducted by genetic genealogist Blaine Bettinger is deeply appreciated by all of us hunting down the relationships with our DNA connections.
Shared DNA statistics from Blaine Bettinger, used by permission
Blaine has created this beautiful chart. His blog has several posts explaining the study which is the source of these new statistics. See http://www.thegeneticgenealogist.com/2015/05/29/the-shared-cm-project/ for all his posts on this study. I had previously discussed his project when recruiting people to add their statistics; apparently he is still taking in statistics so click here to add yours.