The DNA Shuffle

We inherit half our DNA from each of our parents, but that DNA is shuffled in a couple of ways before we get it. This results in our inheriting our parents DNA in roughly 118 separate segments. That number increases by about 71 segments for each additional generation. The number of our ancestors, or at least the number of slots in our family tree, though, doubles every generation. Consequently, by the time we get to the tenth generation, we inherit about as many segments as we have ancestors, and by the twentieth generation, only about 0.1% of our genealogy actually contributes DNA. David Reich:

Yet even if the genealogies are accurate, Queen Elizabeth II of England almost certainly inherited no DNA from William of Normandy, who conquered England in 1066 and who is believed to be her ancestor twenty-four generations back in time.21 This does not mean that Queen Elizabeth II did not inherit DNA from ancestors that far back, just that it is expected that only about 1,751 of her 16,777,216 twenty-fourth-degree genealogical ancestors contributed any DNA to her. This is such a small fraction that the only way William could plausibly be her genetic ancestor is if he was her genealogical ancestor in thousands of different lineage paths, which seems unlikely even considering the high level of inbreeding in the British royal family.

Reich, David. Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past (Kindle Locations 636-643). Knopf Doubleday Publishing Group. Kindle Edition.

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