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  • help with x match

    what dose it mean to have an x match with someone?? how can i know if the matches are from the mother side or father side???

  • #2
    In general, an "X match" simply means you share a segment on the X chromosome with a match. At FTDNA, you will only see an X segment match if you also share matching segments on the autosomes (chromosomes 1-22). Unfortunately, FTDNA will sometimes show "X-match" when there are only very small matching segments on the X, which is misleading. You have to compare your matches using the Chromosome Browser to see how many cM (briefly, cM stands for centiMorgan, a unit of size used for chromosome segments)*.

    Another point that needs to be taken into account with X chromosome matches is, that while most genetic genealogists consider that a minimum of 7-15 cM should be used for matching segments on chromosomes 1-22, BUT for the X chromosome, you should double that amount (so, about 15-30 cM at minimum, to be considered a valid match) due to the way it recombines.

    Thirdly, the X chromosome has a unique inheritance pattern. So, if you have an X-match with a good amount of shared cM, you can use the charts at the following sites, fill in your ancestors in the appropriate spaces (do the same for the match, if they have a tree), and see if that helps you to find a common ancestor. There are different inheritance patterns for males and females; you will have to use the charts to figure out if the match is on your maternal or paternal side. Charts can be found at:You can read more to understand the X chromosome at these websites:*From the FTDNA Learning Center Glossary, a more detailed definition:
    A centiMorgan (cM) is a measurement of how likely a segment of DNA is to recombine from one generation to the next. A single centiMorgan is considered equivalent to a 1% (1/100) chance that a segment of DNA will crossover or recombine within one generation.
    Last edited by KATM; 17 July 2020, 12:28 PM.

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