This utility calculates probable relationship paths based on Autosomal and X-DNA Genetic Distances.

This application only works properly for 2 kits with a non-zero cM result for X.

Please explain what "non-zero cM result for X" means.

  • Welcome to G&FH SE! As a new user be sure to take the Tour to learn about our focussed Q&A format which is quite different from bulletin boards, discussion forums and other Q&A sites you may be used to. Would you be able to include a link to the GEDmatch Relationship Calculator that you used, and where you (presumably) read that "This application only works properly for 2 kits with a non-zero cM result for X", please?
    – PolyGeo
    Feb 27, 2018 at 1:25
  • @PolyGeo the link would be inaccessible to those without a Gedmatch account.
    – user6485
    Feb 27, 2018 at 10:25

1 Answer 1


I assume you're talking about the 'Tier 1' Relationship Tree projection tool. Not many of us are gedmatch.com Tier 1 subscribers.

But a non-zero CM result for X is self-explanatory. The 'X' refers to the X chromosome, which men receive exclusively from their mother (the father gives them a Y-chromosome), and for women a copy is received from each parent. That allows some prediction of how exactly you might be related, as the X-DNA inheritance tree is only a subset of all possible ancestors. For more details, see this article: https://dna-explained.com/2012/09/27/x-marks-the-spot/. Note that the X-DNA ancestor tree depends on the gender of the person being tested.

A centimorgan (cM) is a unit of measurement of DNA strand length. When you share DNA with someone else, this is usually measured in centimorgans.

You can only use this tool between two kits that actually share (non-zero cM) some X-DNA.

  • Yes, Thank you, Tier 1 Relationship projection tool - this answer heped from members of Genetic Genealogy Tips : Looks like the formula they are using to predict the relationship is dependent on both people sharing both an autosomal and xdna matches. So you need to only include pairs of people that have numbers in both adna and xdna. it was understanding what non-zero mean't ,Thanks for your responses, much appreciated. Maureen Feb 28, 2018 at 2:49

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