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Archiver > GENEALOGY-DNA > 2011-02 > 1297539858


From: Ann Turner <>
Subject: Re: [DNA] x chromosome puzzle
Date: Sat, 12 Feb 2011 11:44:18 -0800
References: <4d56a721.86a8e60a.1c5b.108b@mx.google.com>
In-Reply-To: <4d56a721.86a8e60a.1c5b.108b@mx.google.com>


It's due to the different thresholds for matches involving males. Since
males have only one X chromosome, there's no ambiguity about which parent
contributed which allele, and the thresholds are relaxed. The segment does
come through you, but many female-female matches with a similar number of
SNPs and cMs would turn out to be false positives.

If your sons match your mother in the region, the match is coming from YOUR
mother's side of the family. You can see how this works in the Family
Inheritance diagrams for the demo Mendel family, comparing the siblings Ian,
Alan, and Erin to their maternal grandmother Margo Fisher.

Ann Turner

On Sat, Feb 12, 2011 at 7:28 AM, Aggi-Rose Reddin <>wrote:

> Hoping someone here can explain this one for me re a match at 23andme:
>
> woman has a 30cM share on the x chromosome with my 2 sons but nothing
> shared with either myself or my mother.
>
> Also, she is predicted as 4th cousin to my sons.
>
> She is adopted so we can't just figure this out via paper trails.
>
> Is our connection definitely/only/necessarily [?] through my father's side?
>
> And why doesn't she share with me? Is that due to recombination
> effect or something else?
>
> Help?!
>
> Thanks
> AR
>


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