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I am very new to genealogy and I am hoping someone can advise me. Having uploaded my gedcom to Gedmatch, my best one-one match on Gedmatch is with someone who matches on Chr 8 (14.4 cM) and Chr 11 (30.0cM), but there is no match on the X chromosome. I am female and the match is male. Can I assume that the DNA match is therefore on the Paternal line?

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No, you can't assume the match is on the paternal line.

As a female, you have 2 Xs – one from each parent.

As a male, your match has only one X – from his mother.

X-chromosome inheritance is not linear. If you are related to his maternal great grandfather, for example, you will also not share any X-DNA.

The following is a nice chart which highlights the ancestors from which a man inherits X-DNA: enter image description here Source: The Genetic Genealogist

You could easily be related via ancestors in any of the white areas.

Also, for a distant match like this, even if you are related via an ancestor with whom you might expect to share X-DNA, you might not share any X-DNA purely by chance. DNA inheritance is random, with genetic recombination occuring in each generation. After several generations, the 'common X-DNA' might have been diluted such that matching algorithms cannot identify it.

In summary, a negative X-DNA match does not rule out relationship to any of his maternal ancestors. However, a positive X-DNA match would be suggestive that the match was on his maternal side.

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  • Thank you! You comments and explanation were very clear and useful! I like the pedigree chart too. This led me to reading the source : Genetic Genealogist whose detailed explanation has finally nailed it for me! – ShirlB Jan 23 '18 at 12:54
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I would emphasize the second part of Harry Vervet's answer w.r.t. dilution.

Failing to match on the X chromosome is no more significant than failing to match, in this case, on chromosomes 1-7, 9, 10, or 12-22. If your match is male, then it's actually much less significant, since he can only match one half of your X pair, but could match either half of any of the others.

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    The general rule is: lack of a match does not imply lack of a relationship. So: lack of an X-chromosome match does not mean you are not related via an X-inheritance ancestry path. – RobertShaw Jan 24 '18 at 20:29

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