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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.

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

https://github.com/castedo/genomology

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:

https://www.geneheritage.com

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

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  • Thanks for this. Will it work if I don't have the parent's kit (only the grandparent and grandchild)? – Harry Vervet May 14 '19 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 May 16 '19 at 18:00

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