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X chromosome - Webinar - FF

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  • X chromosome - Webinar - FF

    Hi,
    I recently listened to the X chromosome webinar. Thank you in advance for these considerations.

    I am GA for two geographic DNA projects considered isolated / mountainous regions with specific migrations within the last 600 years. I have personally done or crosschecked most of our members pedigrees and have the actual records as documentation. So the pedigrees are fleshed out 6-8 generations as records allow (all siblings/all generations). Our FF results OFTEN show relationships much closer than expected. This frustrates my members (and me too as I have no better explanation. The moderator indicated this could lead to closer related matches.

    Now the X is exciting but I am wondering how the cross over in the small region will impact the X matching. Any thoughts in general? Also, I have laid out four key pedigrees, my own, my mother, her brother and a known 2nd cousin. Everyone's ancestry is from this geographic region.

    I did a table of Who the source of all possible X chromosome COULD be for each person. Next, I compared WHO matched across the 4 pedigrees/table meaning (who they had in common) It does indeed [I][I]point towards the viable candidates for the specific X source.

    Question: I used myself as the base and the others as the comparison. I know they do NOT compare to each other just to me. Is my thought process correct? Do I need to run the chromosome browser through all permutation: Daughter compared to Mother, brother and cousin Then Brother compared To Sister, Niece and cousin? Mother compared to daughter, brother, cousin? Cousin compared to Cousin?

    Thanks again for the feedback.

  • #2
    Please explain. what do you mean, cross over in the "small region"?

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    • #3
      Definition of cross over used in post

      Many of our project members from this small geographic area have common ancestry between each other. They can share a number of different ancestors on their trees with different project members. So, we look for the common ancestor.

      By cross over, I meant that even within our members personal pedigree from this small geographic area, they have the same ancestor or siblings of same of a common ancestor on multiple branches of their OWN pedigree. It is not intermarriage as the degrees of consanguinity were reasonably held to with the exception of dispensations in the various cholera years.

      So when looking at WHO can contribute to the X chromosome, a source can be named multiple times. Will THIS be "magnified" in a sense like we see with FF?

      Thanks.

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      • #4
        Originally posted by KAM View Post

        So when looking at WHO can contribute to the X chromosome, a source can be named multiple times. Will THIS be "magnified" in a sense like we see with FF?

        Thanks.
        Yes, it will. For example, I am seeing Jewish men with close relatives on their father's side who also share sizable X-chromosome blocks from with those matches from their mother's side.

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        • #5
          That also occurs with the small autosomal segments so that a person will share a larger block on one side, and a smaller block on the other.

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