Creating a phased DNA kit using grandparents' kits?


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.

Harry Vervet

Posted 2019-05-12T16:32:03.940

Reputation: 17 763



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.


Posted 2019-05-12T16:32:03.940

Reputation: 186

Thanks for this. Will it work if I don't have the parent's kit (only the grandparent and grandchild)? – Harry Vervet – 2019-05-14T02:45:32.800

Sorry, the code currently only works if there is at least one person from each generation level (i.e. parent also needed). – Castedo – 2019-05-16T18:00:02.250