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Thread: Question about Chromosome 6

  1. #1
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    Question about Chromosome 6

    This is sort of a followup to my other post: https://anthrogenica.com/showthread....s-accurate-now

    So, I think I may have found the source of my and my cousin's unaccounted for 1% regions on AncestryDNA. I took a look at both of our kits on GEDmatch, and noticed my cousin and I have quite a few what I believe to be Ashkenazi Jewish matches. I was intrigued because I thought it might lead me to the source of my cousin's 1% Jewish DNA and my 1% Sardinian DNA. My cousin has many more matches with AJ than me, so I used his kit for the experiment.

    I used a combination of One-to-One comparisons and chromosome paintings on GEDmatch. I noticed that the majority of the Jewish matches all matched at a very specific point on chromosome 6. I examined this chromosome for both myself and my cousin, and I noticed there was a higher than average Mediterranean component on this chromosome compared to other 21; however, the dominant Mediterranean component on mine was West_Med (which I think is common in Sardinians), and for my cousin it was East_Med and West Asian (common in AJ?). When comparing this region one-to-one with my cousin's kit to different Jewish matches, the regions in common were painted as a mixture of Mediterranean and Northern European elements, with every kind of mixture (some were painted predominantly Mediterranean and some were painted predominantly Northern European, while others were pretty balanced). Because of this variance, it made it difficult to determine whether the common ancestor was of European or AJ origin.

    I found it peculiar how many matches were on the same position on chromosome 6, as I had never experienced that with any of my other matches, at least in the volume that it was in this case. I researched chromosome 6 a bit and found that it apparently contains a large part of the immune system and its common for people of different origins to match on it. I'm not too versed in DNA lingo, but based on what I read I got the impression that ancient components are more commonly preserved on this chromosome and it's common to get false matches or at least matches that are not genealogically relevant. It's curious because my cousin and I have virtually no Ashkenazi Jewish matches on AncestryDNA, but many on GEDMatch. My only thought about this was that maybe AncestryDNA filters out these irrelevant matches with their Timber algorithm. Would this be a correct assumption, or is there something I'm missing?

    Furthermore, as I said, chromosome 6 has a higher concentration of Mediterranean components on both my and my cousin's kits. Could this be the source of the 1% Sardinian and European Jewish DNA ancestry is picking up? If so, is this relevant, or just ancient admixture that AncestryDNA is randomly assigning to closest populations in their database?

    Sorry for the long winded response, but I appreciate any response as I'm trying to get the to the bottom of this curious genealogy question.

  2. The Following User Says Thank You to lookiecookie For This Useful Post:

     JMcB (06-26-2020)

  3. #2
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    Yes, Chromosome 6 can be misleading.
    You may find the following helpful https://isogg.org/wiki/Identical_by_descent
    Look for the section on "Excess IBD sharing".
    It also provides links to other resources on the topic you raise.

    For cousin matching many people exclude this region from their comparisons.
    Some DNA companies do too.

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     JMcB (06-26-2020)

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    Quote Originally Posted by Saetro View Post
    Yes, Chromosome 6 can be misleading.
    You may find the following helpful https://isogg.org/wiki/Identical_by_descent
    Look for the section on "Excess IBD sharing".
    It also provides links to other resources on the topic you raise.

    For cousin matching many people exclude this region from their comparisons.
    Some DNA companies do too.
    exactly

    I used to have a small jewish marker on the Chr......but was always told it is wrong ...........after doing BigY it ( "jewish" )disappeared

    I also exclude this chr 6


    My Path = ( K-M9+, TL-P326+, T-M184+, L490+, M70+, PF5664+, L131+, L446+, CTS933+, CTS3767+, CTS8862+, Z19945+ )


    Grandfather via paternal grandmother = I1-L22 ydna
    Great grandmother paternal side = T1a1e mtdna

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     Saetro (06-27-2020)

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