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  • X match comparison

    I have not contacted my potential X match. I have not used any DNA tools, to project relatedness; genealogically or otherwise. I read the X matching tutorial. Where FT DNA does not currently, use the X chromosome for genealogical matching.We are both males. His own surname is Johnson. I have a great grand mother Johnson. She was my maternal, grand-daddy's mother. Her maiden name was Johnson. We show as a 3rd to 5th cousin with our longest shared block of 16.60cm, on chromosome #16. We share a total of 82.91cm.
    We share a total of 55.88cm, on the X chromosome. The longest is 22.33cm from 96602754 to 118788765.
    We share a 7.81cm block from 53161383 to 71344844; a 10.16cm block from 86286266 to 96298324; a 15.58 block from 142597252 to 1496888892. We share a surname. That for myself is 3 generations, before me. I would be the 4th generation. My Johnson surname has been genealogically proven back, to late 1700's Upper SC into Western NC. A distance of 50 to about 75 miles difference. I have mentioned, on these threads. Something about a situation in NC. I have no knowledge of the situation. The X match comparison appears to share a large total amount of the X chromosome. I got the initial impression. I have received a large amount of my X chromosome, from my Johnson great grand mother. My match only shares his own surname. Any thoughts?

  • #2
    Originally posted by brian View Post
    I have not contacted my potential X match. I have not used any DNA tools, to project relatedness; genealogically or otherwise. I read the X matching tutorial. Where FT DNA does not currently, use the X chromosome for genealogical matching.We are both males. His own surname is Johnson. I have a great grand mother Johnson. She was my maternal, grand-daddy's mother. Her maiden name was Johnson. We show as a 3rd to 5th cousin with our longest shared block of 16.60cm, on chromosome #16. We share a total of 82.91cm.
    We share a total of 55.88cm, on the X chromosome. The longest is 22.33cm from 96602754 to 118788765.
    We share a 7.81cm block from 53161383 to 71344844; a 10.16cm block from 86286266 to 96298324; a 15.58 block from 142597252 to 1496888892. We share a surname. That for myself is 3 generations, before me. I would be the 4th generation. My Johnson surname has been genealogically proven back, to late 1700's Upper SC into Western NC. A distance of 50 to about 75 miles difference. I have mentioned, on these threads. Something about a situation in NC. I have no knowledge of the situation. The X match comparison appears to share a large total amount of the X chromosome. I got the initial impression. I have received a large amount of my X chromosome, from my Johnson great grand mother. My match only shares his own surname. Any thoughts?
    Hi Brian,
    I think you and this cousin must be related on the X chromosome but the cousin did not get his X match from his Johnson line (directly anyway) because the X segment did not follow an all-male pathway in the line of descent in his pedigree. So I would be looking for other surnames too. You really do need to inspect his pedigree and make contact with him. Start with the X pattern of inheritance first just because this is a strong clue and you may not have to evaluate as many lines back in time. Try to find that geographical location that matches on the X pathway. If there is no surname match but there is a strong town match, then that is when brick walls are sometimes broken down. His mother's X lines are important here.

    When you look at your probabilities, there is a chance you did get a large amount of your X from your Johnson great grandmother. A female to male to female to male transmission has the highest odds but that still does not mean it could not be something else like male to female to female to male. That happens too. I think I would follow the odds here because the X is strong in your case so therefore males were probably involved in the transmission. Very few females broke up the segment even though females have to be involved every other generation at the very least: http://www.thegeneticgenealogist.com...mosome-charts/

    Often the X segment is inherited from the same set of ancestors as the autosomal segment was, but that is not always the case. You can match more than one ancestor in your matching partner's pedigree too. If it is a fairly close ancestor in common though, then often the autosomal plus X match traveled together in the same ancestors. Colonial ancestors do pose a problem because often we are related on several lines, so endogamy and pedigree collapse can be involved. More than one X segment could even mean different X lines. The predicted relatedness (which FTDNA only bases on the autosomes) is often not correct and is usually farther back in time than stated, but in your case you definitely need to look because you have more than one chromosome involved and the X was not taken into account when predicting 3rd to 5th cousins. The 22 cM might need to be added to the 10 cM block to form one long segment.

    I would be curious to see if you can find a name or location in both trees that is a strong X match. Males are naturally phased because they only have one X segment to share. Long cM matches in males can be very helpful in predicting IBD but not always close in time. Let us know how it works out.
    Good luck,
    Kathy

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