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Theoretical vs. Actual Shared DNA

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  • Theoretical vs. Actual Shared DNA

    Your Genetic Genealogist has an interesting blog post comparing the amount of shared DNA between known cousins. The actual amounts of shared DNA vary, but they're not too far off from the theoretical expected values. There are chromosome diagrams showing the matching segments, which might be useful to help understand how it works (especially if you're a visually-oriented person like me). Although the amounts shared are similar, the segments each cousin shares with each other are different. That's why you might match a person, but someone as close as your sibling doesn't, because you inherit different parts of your parents' DNA.

  • #2
    Thanks for posting that. I always find real life examples, such as that blog posting, very useful to illustrate how random recombination of DNA results in slightly different amounts of shared DNA with cousins, even among siblings.

    I sent a link to that posting to the wife of my 2nd cousin, twice removed to help her understand. She and her husband just tested at 23andMe. She already has her results, but her husband had to submit a new sample because the first one had insufficient DNA. She is a very diligent genealogist and very excited about using 23andMe results for her and her husband's family trees. Also, one of my 2nd cousins should get her 23andMe results in the next week or two, so this posting by The Genetic Genealogist will come in handy for her too.