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  • Dilution

    My brother and I are working to discover our ancestors, and at this time we are looking to determine Native American ancestry. My brother ordered the DNAWorks test yesterday from I note Dr. Blankfeld's response to Redheaded1 regarding which test to use to determine her husband's Native American ancestry in a pattern that changes hands from women to men in 6-7 generations. The response stated that a DNAPrint test might be informative, if the dilution were not too high. We are seeking information as follows:

    My brother
    Our (his) mother
    Her father
    His father
    His mother
    Her Native American parent (don't know which of two was Native American)

    My brother had a different father than me. My brother's father descended from purely Scottish folk on both sides, whereas my father descended from Anglo, Celtic and possibly Native American folks. Our mother is descended from Anglo, Celtic and, from above, possibly Native American folks.

    My question is, given the distance to the Native American parent through our mother, and given the fact that my brother's father descended from a homogeneous lot of folk, is there a possibility that the Native American ancestry in my brother's sample will be obscured or "diluted" by the Scots to the point that it will not appear in the results? Please explain more about "dilution" in our fact pattern. Please also tell us what more, if any, we might gather from me having a DNAPrint done. Thank you.

  • #2

    There's no such a thing of one ethnicity being obscured by another. The concept of dilution is purely mathematical. The autosomal DNA (that is analyzed for the DNAPrint test) consists of the 22 pairs of chromosomes in individual A that resulted from the combination of the father's and mother's own 22. Mathematically, individual A's 22 pairs has 50% information from each parent. Since each parent received 50% information from their own parents, this means that A has 25% from each grandparent. Or, 12.5% from each ggparent. Or 6.25% from each gggparent.
    Since we are not dealing with something precise, there's a margin of error in those numbers. That's why we say that if the full blooded ancestry occurred beyond 6 generations ago, it is very possible it got diluted to the point that the current DNAPrint test may not detect it.
    Here's an easy way to see it:
    6 generations ago....100% full blooded ancestry
    5 generations ago....50% ancestry
    4 generations ago....25% ancestry
    3 generations ago....12.5% ancestry
    2 generations ago....6.25% ancestry
    current generation....3.125% ancestry

    Maybe in the future a test will be developed which will allow a higher degree of detection. But right now, that's how the concept of dilution works for the DNAPrint test.
    I hope this clarifies.
    Max Blankfeld
    Vice-President and COO @ Family Tree DNA
    A Gene by Gene Company