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Old 23rd July 2017, 04:42 PM
FuriousGeorge FuriousGeorge is offline
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Investigating possible IBC IBS realtionships / false positives

I'm more interested in ancient migrations than finding more cousins, as I'm already fortunate to have many.

Having had both of my parents tested, I'm now able to see that I have a portion of matches that don't match either of my parents.

I assumed that they were necessarily false positives, but upon a little research I discovered that it could mean that the relationship is so distant that they could be related to both of my parents, even if my parents are not related in genealogical times.

Having said that, my maternal grandparents are from an adjoining "counties" within the same "state" in Spain as my paternal grandparents, maybe 60 mi / 100 km apart, and the same is true for all of their respective ancestors as far as we know (which is pretty far on both sides).

That would suggest that on the super-genealogical scale they must share some common ancestry, and the similarity of their 'ethnicity testing' across 4 services seems to confirm that.

So I became more intrigued by my closest match not in common with either parent, who is from Sweden, and knows of no Spanish heritage. The relationship is estimated as "4th to distant". She shares only 38 cM with me, with a longest segment of 10. The chromosome browser lists 13 other shared cMs < 10 in length, averaging about 2 cM. Despite the weakness of the match, outside of my parents and a known 2nd cousin, she is my 6th closest match out of ~130.

I'd read about phasing, and attempted to use the chromosome browser to clarify our potential relationship. I expected to be able to verify which segments from each parent were recombined to make the match. Unfortunately, in practice (and probably for good reason) it shows each parent as matching on 100% of my cMs, not 50%.

In other words, when the 4 sets of visual representations of our respective chromosomes are stacked vertically there is no way to tell which part she shares with which parent, as both parents look like my identical twins, with everything matching me.

Any pointers are appreciated.

Last edited by FuriousGeorge; 23rd July 2017 at 05:00 PM.
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Old 23rd July 2017, 11:20 PM
ech124 ech124 is offline
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If you have not done so already, load yourself and your parents to the free site www.gedmatch.com.

You might find your Swedish match there already, but if not, try to get them to upload also.

Gedmatch allows fine tuning the settings and if you know the kit numbers, you can compare any kit to any other kit. It might be as simple as on FTDNA the SNP count being a notch below the cutoff.
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Old 25th July 2017, 01:35 PM
FuriousGeorge FuriousGeorge is offline
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Quote:
Originally Posted by ech124 View Post
If you have not done so already, load yourself and your parents to the free site www.gedmatch.com.

You might find your Swedish match there already, but if not, try to get them to upload also.

Gedmatch allows fine tuning the settings and if you know the kit numbers, you can compare any kit to any other kit. It might be as simple as on FTDNA the SNP count being a notch below the cutoff.
I have phasing batched over there. One-to-one compares work already, one-to-many will take a bit longer. However, my Swedish friend does not show up.

I could ask her if she would be interested in adding herself, but I was hoping there was some way to confirm this within ftdna already.

It seems from what I've read that 38 cM on 14 segments with a largest of 10 cM in common is more than usual match for this type of match that is not in common with either parent.

FTDNA's learning center uses the following example to explain how recombination might work, and the nature of the relationship between the matches.

https://www.familytreedna.com/learn/...either-parent/

Quote:
Margo’s father Peter shares a common segment with Ed Blet that starts at SNP Set #2006 and ends at SNP Set #2011. This forms a small segment that runs from 112510 to 1524189 and is 4.39 cM. Peter and Ed also share other small segments for a total of 18 cM. The likely source is a remote relationship that predates the genealogical time frame.

By coincidence, the two smaller segments from each of Margo’s parents have formed a compound segment that looks like a larger segment. Because Margo also inherited many small shared segments (with Ed) from each parent, the program triggers a match calculation for her but not her parents.

Such matches will most often fall into the Speculative Relative category. The true relationship will be on the more remote end of the range. That is, the parents and the child almost surely share a relationship with the remote cousin within twenty generations. However, the relationship is unlikely to be from genealogical times.

Last edited by FuriousGeorge; 25th July 2017 at 02:21 PM.
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