I was lucky in that I was able to DNA test both paternal grandparents, as well as my maternal grandmother before she died last year. I have also tested my mother, but unfortunately my other grandfather died a few years ago. Nevertheless, in theory I should be able to nearly completely phase my DNA matches into each grandparent.

GEDmatch has its phasing tool but this only works for parent-child phasing, not grandparent-grandchild phasing.

I can phase my mother's matches using her mother's kit, but this doesn't help with phasing my matches. I have not tested my father since I was able to test both his parents.

Any suggestions on how this might be achieved? I am open to using tools on GEDmatch or other resources.

1 Answer 1


I have written an R library to do exactly what you are calling "grandparent-grandchild phasing". You can find the (open source) code at:


In addition to the R code, there are two PDF files on that page which show the math used in this software to estimate which segments of DNA come from which grandparent.

I also run a commercial online reporting service which uses the above open source code:


This service will calculate the % of grandparent DNA in a grandchild and put the calculations in a pretty pie chart.

  • Thanks for this. Will it work if I don't have the parent's kit (only the grandparent and grandchild)?
    – Harry V.
    Commented May 14, 2019 at 2:45
  • Sorry, the code currently only works if there is at least one person from each generation level (i.e. parent also needed).
    – Castedo
    Commented May 16, 2019 at 18:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.