How many genetic ancestors do I have?

Which ancestors does your DNA come from? An interesting article from UC Davis Genetics department about DNA inheritance.

gcbias

In my last couple of posts I talked about how much of your (autosomal) genome you inherit from a particular ancestor [1,2]. In the chart below I show a family tree radiating out from one individual. Each successive layer out shows an individual’s ancestors another generation back in time, parents, grandparents, great-grandparents and so on back (red for female, blue for male).

family_tree
Each generation back your number of ancestors double, until you are descended from so many people (e.g. 20 generation back you potentially have 1 million ancestor) that it is
quite likely that some people back then are your ancestors multiple times over. How quickly then does your number of genetic ancestors grow, i.e. those ancestors who contributed genetic material to you?

Each generation we go back is expected to halve the amount of autosomal genetic material an ancestor gives to you. As this material…

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