Help:X-Chromosome DNA Tests

Categories: DNA

Usage of X-chromosome DNA testing (abbreviated xDNA) for genealogy is relatively new. These are not generally separate tests. Family Tree DNA offers an xDNA STR test but it is not very useful for genealogy.

The autosomal tests from the major testing companies (23andMe, AncestryDNA, and Family Tree DNA's Family Finder) now include xDNA matches.

What's Tested

Like the Y chromosome, the X chromosome is part of the sex-determining 23rd chromosome. Males have an X and a Y. Females have two Xs.

X-chromosome inheritance is not as simple to understand as the Y chromosome, which follows a direct paternal line. Males inherit one X chromosome from their mother. Females inherit one from their mother and one from their father.

To see your family's X-chromosome inheritance, click to your DNA Ancestors page.

Why to Test


Because of the specific pattern of inheritance, you have a smaller number of possible shared ancestors with xDNA matches than with general autosomal matches.

The xDNA matches are a subset of the autosomal matches. Your possible shared ancestors are a subset of your tree.

When you contact an xDNA match, show them the xDNA section of your DNA Ancestors page. Someone there is an ancestor they share (unless of course your tree is incomplete or imperfect).

Usage on WikiTree

See the DNA Features for how you can use special WikiTree tools and widgets to collaborate with your matches.

To confirm a relationship using xDNA matching then the shared segment needs to be 6 cM or greater if one of the matches is female. If both matches are male then the segment only needs to be at least 1 cM. For more information see:

We are now working on expanding our xDNA capabilities to make these results easier to use for confirming ancestry.

See also: Autosomal DNA Tests, Y-Chromosome DNA Tests, Mitochondrial DNA Tests.

This page was last modified 15:07, 23 May 2017. This page has been accessed 90 times.