Political Animal, Physician, Goofball, and All Around Nerd. · Author has 10K answers and 234.5M answer views · 6y ·
You are not related to large numbers of your ancestors.
The easiest way to explain this concept is this:
- You’re getting about half your DNA from your mom and dad (ignoring mitochondrial DNA).
- If you go back one more generation, you’re getting a quarter of your DNA from each grandparent on average. It’s not actually 25% from each grandparent.
- For each chromosome you inherited from your mother, there is a 50% probability that it came from your maternal grandmother. It’s a coin toss.
- Now imagine that you are tossing a coin 22 times in a row. It’s fairly unlikely that you will end up with 11 times heads and 11 times tails. That’s how it is with your chromosomes. It’s actually possible to have no chromosome from one of your grandparents, but that probability is something like 1 in 8 million. It would look like this:
- Now, it’s actually a bit more complicated than that. You don’t inherit whole chromosomes from your parents. You get a lot of mixing:
- That said, the more generations you go back, the more you ensure that you’ll get a lopsided contribution from some ancestors and none from others, because the recombination process is pretty random.
- By the time you get to 5 generations up (great-great-great-grandparents), you have a 1 in 8 chance of having no DNA from at least one of your ancestors.
- By the time you get to 7 generations up, it’s almost entirely likely that you won’t share any DNA from at least one of your ancestors.
What this means is that whenever you hear that you’re related to Charlemagne or Genghis Khan, it’s probably not true. The DNA of that illustrious ancestor of yours is so diluted by the time it gets to you that you’re essentially not related.
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