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
A long time ago I wrote a post about the Are Your Parents Related Tool at GEDmatch, a tool which looks for places in your DNA test results where you have a long run of identical DNA on each side of a chromosome pair. In other words, you have segments of the exact same DNA from each parent. My theory, which has so far worked in practice, is that you multiply the cM of matching DNA by 4 to get the amount shared by your parents. I will be interested to see how the numbers Blaine collects compare.
I have been collecting the numbers for 25% relationships (half sibling, aunt, uncle, grandparent, ..) so add yours by clicking here.
I also have been collecting the amount shared on the X chromosome for close relatives which I posted about at http://blog.kittycooper.com/2015/08/help-me-collect-x-chromosome-data/
Thanks to everyone who added their family’s numbers!