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Family Finder Advanced Topics Advanced discussion about Family Tree DNA's Family Finder Product.

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  #1  
Old 25th June 2017, 08:39 AM
mcdowc1 mcdowc1 is offline
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Join Date: Aug 2015
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Issue with maternal matching

I've just noticed something unusual with maternal matching and wondered whether it was a bug or is there something I'm missing.

I have both my mother's and my own autosomal DNA uploaded - originally tested by Ancestry and then transferred.

I noticed two matches. From their trees, they appear to be father and son. They are both administered by the same email account and the "match dates" are within a day of each other which makes me think their tests were done at the same time.

If I look at Chromosome Browser then the shared segments are virtually identical - which you would expect.

However, the Father appears with the red maternal icon indicating that it is from my mother's side, the son's does not.

If I log in using my mother's kit number then only the father is shown as a match which is it least consistent.

I'm struggling to understand how this can be anything other than a bug and wondered if anyone else had come across something similar or could explain it.
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Old 25th June 2017, 09:55 AM
prairielad prairielad is offline
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Location: Canada
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What size is the segment between your mother and each of matches (cM size for both)?

Are both matches over 9cM?


https://www.familytreedna.com/learn/...tching-system/
"While the matching is done using a variety of formulas based on phased DNA, there is currently one threshold that is hard-coded. The current version of the Family Matching system takes into account only those blocks that are equal to or longer than 9cM. As we acquire more data, this number over time is likely to change and become lower.

Due to several reasons, including the hard-coded 9cm threshold, many matches will show up on an individualís match page yet do not include the maternal or paternal icon. These matches may still be valid, but have not yet been assigned based on the phased Family Matching criteria today."

Last edited by prairielad; 25th June 2017 at 09:59 AM.
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  #3  
Old 25th June 2017, 09:59 AM
ech124 ech124 is offline
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Join Date: Jul 2011
Posts: 198
Sounds like this may be an issue of the new matches being very close to the matching threshold.

Latest ancestry transfer chips will only show 3rd-5th cousins at the most.

From your account, please list total and largest cM amount 1. father 2. son.

From your mother's account list total and largest cM amount for father.

For marginal cases, even a 1 cM difference can put you into a different match category. All companies have to choose the line in the sand somewhere.

Last edited by ech124; 25th June 2017 at 10:08 AM. Reason: Chip sentence
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Old 25th June 2017, 10:50 AM
mcdowc1 mcdowc1 is offline
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Join Date: Aug 2015
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Thanks to both for getting back so quickly. That certainly sounds like a logical explanation as I transferred my own DNA in 2015 but only transferred my mother's earlier this year when transfer from Ancestry was reinstated. However the thresholds sound like they are slightly higher than 9 cM.

On my kit, I have shared segments of 12.13 cM and 11.79 cM with the father and son respectively. On my mother's kit, she shares an 11.02 cM segment with the father.

I suppose the take away from this is that I shouldn't assume that all the matches that don't show up as being common with my mother are automatically matches with my father (he died some years ago and so I don't have his DNA).
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  #5  
Old 25th June 2017, 11:23 AM
ech124 ech124 is offline
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Join Date: Jul 2011
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Yes, it sounds like your mother has reduced matching. She probably has fewer matches than you do. You cannot assume a non-maternal match is automatically paternal.

Out of my own account (I have full matching), I have a 4th-Remote cousin listed as total 72 cM, largest 12 cM. Such a person would not make the cut if I was a recent transfer kit.
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  #6  
Old 25th June 2017, 11:52 AM
prairielad prairielad is offline
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Location: Canada
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Can not find it at the moment, but I believe transfers will not show the 4th to Remote range, so depending on level this match is, like ech124 mentions, the son may not show on mothers list due to Ancestry chip version
pre May 2016 Ancestry chip was very similar to FTDNA, after May it changed, latest chip excludes distant matching due to number of compatible SNPs which can be compared.

Believe if one wants the full matching (distant cousin) one would have to upgrade transfer to Family Finder......which I thought was offered at a discount, but do not see it in the upgrade options of transfer kits....
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