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2nd cousin on father's side an X-match?

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  • 2nd cousin on father's side an X-match?

    I really don't understand the x-match. I mean REALLY don't understand it. My half- 2nd cousin and I are both females. Her grandmother and my father were half siblings(same father-different mothers). Her FATHER is my half 1st cousin. What does it mean that we are x-matches? ANY explanation fit for a 2 year old would be helpful. Thanks.

  • #2
    You need to tell us how they match on the X: how many cM is the largest matching segment? Is there more than one segment, and how big is it (or they)? To find out, select your half- 2nd cousin in your match list, and click on the Chromosome Browser button, to see the size of the match on the X chromosome. The label "X match" can be misleading, because FTDNA will show X matches regardless of how small the segment is, so you do need to check. You can disregard the X match if the segment is very small.

    In general for X-matches, you need a segment that is about twice as big as what would be considered the minimum size on another chromosome, to be considered Identical by Descent (IBD). Example: if you usually use 7 cM as a minimum for largest segment size (actually considered low nowadays), you would need at least a 15 cM segment on the X. Many people use 10 cM, or even 15 cM, as a minimum largest segment size to use for matches, so that would be 20cM or 30 cM for X matches.

    Overall on all chromosomes, your half second cousin probably shares about an average of 112 cM with you, or within a range of 30-215 cM, according to the DNA Detectives Autosomal Statistics Chart.

    Last edited by KATM; 17th February 2019, 08:10 AM.