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X-DNA Advanced Advanced topics about X-Chromosome matching and anthropologic blocks based on SNPs and/or STRs.

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Old 18th August 2017, 10:53 AM
MMaddi MMaddi is offline
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Originally Posted by alphavisions View Post
I know a lot of people have this same opinion, but if you use logic, pool A has Xmatches and therefore, the rest is pool B - nonXmatches. Thus, it follows that if you are not in pool A, you must be in pool B. So I think there is something here to investigate. Unless you can show us why it is not strong evidence? do you have an example?
prairielad and ltd-jean-pull gave you real-life examples.

While a recombination of the two x chromosomes, one from her father and the other from her mother, is what a woman usually passes on to her children, there are known cases, not just for prairielad and ltd-jean-pull, where an unrecombined x from either the the maternal grandfather or grandmother is passed on whole to the child by his/her mother. You would not know this is the case in your situation unless you have tested the maternal grandparents and their grandchildren, as prairielad has done.

So, he knows by mapping the x segments that the maternal grandfather did not contribute any xDNA to two out of three sibling grandchildren. You don't have that information until you do the same, which is why you can't safely assume what you're assuming in this thread.

Last edited by MMaddi; 18th August 2017 at 11:02 AM.
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Old 28th August 2017, 06:35 PM
mabrams mabrams is offline
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As an example of X non-matching....

My mother has a third cousin, so they share a gg gm, born in 1813. So we have detailed trees and plenty of census and other records.

My mother shares 61 cM with her third, so very reasonable.
My mother also shares a Matching mtDNA of GD = 0 with her third cousin. So a double DNA confirmation.

The mtDNA path coincidentally follows an X path. Although they should share some X DNA, 12 cM, they don't. Not even 1 cM. Nada. Zero.

So not all X cousins share X DNA.

Last edited by mabrams; 28th August 2017 at 06:40 PM.
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Old 29th August 2017, 08:22 PM
alphavisions alphavisions is offline
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While using gedmatch testing on 2 nonXmatches, they gave this information about non-Xmatching which I feel comfortable confirms there is some value to nonXMatches:

Based on X-DNA Genetic Distance, there is no relationship through the X-Chromosome. This means that the ancestry of one or both of these 2 individuals probably has one or more Father-to-son generations that has blocked the transfer of X-DNA. That eliminates possible relationship paths that do not contain father-son generations.

Feel free to use the information as you desire.
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