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Thread: Family Finder results

  1. #21
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    FF.jpg

    This photo shows how Family Finder calculated my closest cousin match. Notice the small matching segments <5cM and SNPs which are <700.

    What confuses me is I have read any matching segments below 7cM and 700 SNP could be noise. Recently there was a conference in Europe in which a lecturer stated anything below 10cM could be a false match, if all this is true then why does Family Tree DNA use small matching segments in their calculating relationship?

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     Tįltos (03-22-2014)

  3. #22
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    @Caesarea yes it is confusing. Here is a picture of my match that FTDNA's prediction has me puzzled for the same reason.

    Chromosome Browser Data.png
    Last edited by Tįltos; 03-22-2014 at 03:41 PM.

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  5. #23
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    I realized gedmatch has a reverse e-mail lookup feature so I went through my Family Finder matches until I found gedmatch kits. Counting only the kits that matched e-mail address *and* name (since some e-mail addresses had multiple kits associated with them), I found about 4 or 5 out of 40. None of the results in One-to-One (using low thresholds like 350 SNPs and 2 cM) matched up to Family Finder's results. So I'm concluding that Family Finder's results for me were completely bogus. I don't know if they were just bugs in the system or they gave me someone else's results.

    Based on this experience I would take FF results with a grain of salt unless verified with Gedmatch and/or 23andMe. I'm pretty disappointed in FTDNA. I'm not sure how serious to take this company for future tests anymore. If they could mess this up, they could potentially mess up anything.

    On the other hand, my raw data seems to correspond with my 23andMe raw data and Geno 2.0 gave me the same haplogroups as 23andMe.

    I think it's high time I gave a donation to gedmatch considering their free service is superior to the paid services in both scope and accuracy.
    Paternal - Y-DNA: J2b2* (J-M241) Z2432+ Z2433+ Y978+ (J2b2a2b1*) (Hidden Content ) (YFull: YF02959) (FTDNA Kit B6225), mtDNA: M18a* (FTDNA Kit 329180) (YFull: YF63773)
    Maternal- Y-DNA: R1a1a1b2a1a2c2d5a* L657+ Y7+ (R-Y16494*) (FTDNA Kit 311047) (YFull: YF68408), mtDNA: Hidden Content (FTDNA Kit B6225) (YFull: YF02959) (Mother's Mother's Father: R1a1a1b2a1a2c2* Y7+ Y29+ (R-Y29*) (FTDNA Kit 329181) (YFull: YF65256))

  6. #24
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    My experience with family finder was positive .Actually i have found 2 real relatives(two fourth cousins once removed) through them which itself was surprising considering so few have tested and i think 1 or 2 more could be potential relatives including my 2nd closest match in ftdna but i couldnt so far find how .
    Direct comparison with family finder and gedmatch wont do good because both use different kind of algorithms . But from what i noticed i am getting more matches in gedmatch(even if i consider just ftdna matches) and most are not potential relatives . And with a single common match i am getting a larger matching segment in ftdna than gedmatch .

  7. #25
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    Quote Originally Posted by Caesarea View Post
    FF.jpg

    This photo shows how Family Finder calculated my closest cousin match. Notice the small matching segments <5cM and SNPs which are <700.

    What confuses me is I have read any matching segments below 7cM and 700 SNP could be noise. Recently there was a conference in Europe in which a lecturer stated anything below 10cM could be a false match, if all this is true then why does Family Tree DNA use small matching segments in their calculating relationship?
    if you have at least one segment above 7cM and 700 SNP then all the other small ones are included in the count. then a second threshold comes into play - the total length of the common segments should be above 20cM.

    If there is not even one segment above 7cM and 700 SNP then no match.
    If you have a single segment above 7cM and 700 SNP and no other segments on the other chromosomes - then again this is not a match.

    In practice due to recombination there is one or two big segments and a lot of smaller segments across the other chromosomes. the more "supportive small segments" the better. So the segment above 7cM and 700 SNP pulls in the picture the rest .....

  8. #26
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    This is what I was referring about:
    http://youtu.be/Jtpe6u2J5ps?t=18m1s
    The chart displayed is interesting. If 4cM is 99% false positive then why is FTDNA using small segments in calculating relationship????

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  10. #27
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    Quote Originally Posted by Caesarea View Post
    This is what I was referring about:
    http://youtu.be/Jtpe6u2J5ps?t=18m1s
    The chart displayed is interesting. If 4cM is 99% false positive then why is FTDNA using small segments in calculating relationship????
    Thanks for posting the video. It's interesting to note how low the reported IBD estimates are, especially in the 4-8cM range. I recall a thread on 23andMe, by the user MiTuCents, discussing a fairly recent paper where the authors determined that matches at 6cM are likely to be real. Small segment matches are usually false positives, but even 4cM segments are still IBD 1/3 of the time:

    http://arxiv.org/abs/1311.1120

    MiTuCents provided a helpful summary, reposted below for those without a 23andMe account.

     
    TITLE:

    New Paper: 4cM Matches are usually wrong in unphased data (which 23andme uses)

    An important paper just came out regarding false segments seen when using non-phased data and segments of 4cM or smaller.

    I have analyzed the paper and attempted to translate it's findings into plain English below.

    BOTTOM LINE:

    Unphased data such as 23andme, FamilyTreeDNA (everyone, really) uses is more often inaccurate for smaller segments. Specifically:

    4cM segment matches with strangers are only real (IBD) 33% of the time. 67% of the time they are false-positives (pseudo-segments) caused by using unphased data.
    6cM segment matches with strangers are usually real.

    So DNA Relatives with a 7cM threshold (as well as a number of SNPs in the segment threshold) are very likely real IBD and those tiny 2cM, 3cM, 4cM segments that people are seeing in Gedmatch etc. are likely (67% of the time) *not* real (IBD).

    ABSTRACT URL:
    http://arxiv.org/abs/1311.1120

    FULL TEXT URL:
    http://arxiv.org/pdf/1311.1120v1

    PAPER TITLE: "Reducing pervasive false positive identical-by-descent segments detected by large-scale pedigree analysis"

    MY TRANSLATION INTO ENGLISH FROM TECHNO-SPEAK:

    Study looked at segments on Chromosome 21.

    A total of 25,432 individuals of European ancestry were used in the study.

    Of this total, they used 2,952 Mother/Father/Child "Trios" in order to be able to phase the child's results. The rest of the people in the study were (presumed) unrelated people (what I will call "strangers") used to identify possible segment matches with the child for further analysis.

    In the 2,952 Mother/Father/Child Trios they found 13,307,562 2cM-4cM segments that the child matched with one or more of the "strangers".

    They then analyzed how many of these segments were also shared by the child's parents (meaning that they are real segments IBD (Identical By Decent)) and found the following:

    14% of the segments that the child matched with the stranger were found in a parent. (Could be identified as real IBD segments)
    25% of the these segments were partially found in a parent (a shorter "truncated" segment was found in a parent)
    61% of these segments were not found at all in the parent.

    They checked all of the segments not completely found in the parent to see if testing errors (mis-calls, etc.) or other "false positives" could account for it. They found that testing errors could only account for 3% of the differences (97% were real differences in the segments).

    They decided to allow that some of the 25% segments seen partially (truncated in) the parent were probably real, and a result of difficulty in determining start and end points for segments (possibly due using SNP data and different and microdeletions, insertions, etc.?). Specifically, they said that 80% of these were likely real, so 20% were likely not real. (20% of 25%) + 61% = 66% which they rounded up to 67%.

    They put the reason for the likely false segments between parents and children as being due to testing services using unphased data, such that the child has a segment which is a combination of segments from both parents and, in the child, appears that it *could* be a real segment but, in reality, is not. (What I call a "pseudo-segment.")

    Other Data Found:

    Of all segments found between the child and a stranger, over 98% were shorter than 4 cM. So only 2% of all matches between the child and a stranger were 4cM or more.

    Most segments longer than 6cM are real segments, but this correspondence "drops rapidly as segment length is reduced."

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  12. #28
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    Does anyone know how many SNPS overlap between Family finder and 23andme chips?

  13. #29
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    Quote Originally Posted by Baibars View Post
    Does anyone know how many SNPS overlap between Family finder and 23andme chips?
    For V4 : Family Finder, there are approximately 305,000 autosomal SNPs in common.

    http://www.yourgeneticgenealogist.co...ir-new-v4.html
     

    Other ancestral Y lines:

    E1b-M81 Ukraine (Ashkenazi)
    E1b-V13 England
    I1-M253 Ireland
    I2-M423 Ukraine
    R1a-L176.1 Scotland
    R1b-L584 Syria/Turkey (Sephardi)
    R1b-L20 Ireland
    R1b-L21 (1)England; (2)Wales?>Connecticut
    R1b-L48 England
    R1b-P312 Scotland
    R1b-FGC32576 Ireland

    Other ancestral mtDNA lines:

    H1b2a Ukraine (Ashkenazi)
    H6a1a3 Ukraine
    K1a9 Belarus (Ashkenazi)
    K1c2 Ireland
    V7a Ukraine

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  15. #30
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    My grandfather's matches with longest block:

    2nd Cousin - 4th Cousin / 66.73 Longest Block: 17.05 (Armenian)
    3rd Cousin - 5th Cousin / 36.25 Longest Block: 14.12 (Hemshin)
    4th Cousin - Remote Cousin / 30.25 Longest Block: 11.01 (Hemshin)
    4th Cousin - Remote Cousin / 35.23 Longest Block: 10.69 (Armenian)
    4th Cousin - Remote Cousin / 33.14 Longest Block: 10.19 (Zaza)
    5th Cousin - Remote Cousin / 23.20 Longest Block: 12.55 (Northeast Turk)
    5th Cousin - Remote Cousin / 28.47 Longest Block: 11.78 (Hemshin)
    5th Cousin - Remote Cousin / 23.30 Longest Block: 11.18 (Armenian)
    5th Cousin - Remote Cousin / 35.94 Longest Block: 9.01 (Hemshin)
    5th Cousin - Remote Cousin / 28.28 Longest Block: 8.70 (Pontic Greek)<<< New match
    5th Cousin - Remote Cousin / 22.03 Longest Block: 8.50 (Anglo European)
    5th Cousin - Remote Cousin / 21.69 Longest Block: 8.31 (Balkar)
    5th Cousin - Remote Cousin / 28.97 Longest Block: 7.93 (Hemshin)
    5th Cousin - Remote Cousin / 23.33 Longest Block: 7.92 (Italian)
    5th Cousin - Remote Cousin / 26.64 Longest Block: 7.87 (Armenian)


    My grandmother's matches with longest block:

    5th Cousin - Remote Cousin / 27.75 Longest Block: 12.29 (Northeast Turk) <<< New match
    5th Cousin - Remote Cousin / 26.08 Longest Block: 9.94 (Armenian) <<< New match
    5th Cousin - Remote Cousin / 26.43 Longest Block: (Northeast Turk)
    5th Cousin - Remote Cousin / 25.77 Longest Block: 9.41 (Armenian) <<< New match
    5th Cousin - Remote Cousin / 26.86 Longest Block: 8.74 (Hemshin)
    5th Cousin - Remote Cousin / 24.69 Longest Block: 8.40 (Armenian)
    5th Cousin - Remote Cousin / 25.52 Longest Block: 8.34 (Georgian)
    5th Cousin - Remote Cousin / 23.63 Longest Block: 8.26 (Hemshin)
    5th Cousin - Remote Cousin / 27.84 Longest Block: 7.78 (Anglo European)

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