X-DNA bug

[Reidar]

I have 3 first cousins, they are all full brothers. They have all strong match on the X-DNA, but no full matches (195.95 cM). But all of them get full matches on the X-DNA with a woman who is totally unknown to all of us. This looks totally absurd to me, it looks as a serious bug. From what we know about the X-DNA, this seems as an impossible result. Has anyone experienced bugs of this kind??

[John McCoy]

There have been several similar reports here recently. I believe at least a few of them were reported to FTDNA customer service and found to be false matches, due to some sort of technical issue (the nature of which I don't think has been explained). If the unknown match does NOT share significant autosomal DNA, yes, it is extremely unlikely that the full X match is real.

[georgian1950]

You could construct a synthetic kit for a female which would have an X-match with every male kit. GEDmatch probably needs better filters on what it allows.

[ghamilton]

I just came across a similar situation with an x-match with an unknown female person with whom my match statistics are the same as I have with my mother. Neither my mother nor my sister show an atDNA match with this other person.

My match with my mother:

• Genomic Position: 1370495 - 154570039
• Shared cM: 195.93
• SNPs: 18092

My match with the female person to whom neither my mother nor I have at atDNA match:

• Genomic Position: 1370495 - 154570039
• Shared cM: 195.93
• SNPs: 18092

And just for a cross-reference, my x-Match with my sister:

• Genomic Position: 33039414 - 67881743
• Shared cM: 31.20
• SNPs: 3000

and

• Genomic Position: 115483021 - 137934767
• Shared cM: 26.61
• SNPs: 2850