How many genetic ancestors do you have?

> The number of genealogical ancestors you have n generations is 2n: 2 parents, 4 grandparents, 8 great-grandparents, and so forth. The only way to have fewer is if some of them are the same person.

They leave out that this effect that "some of them are the same person" is inevitable, even pervasive, past a few generations. Never mind that the number of "genealogical ancestors" rapidly becomes larger then the number of humans alive at the time, it's almost certain that your * 10 grandparents didn't travel much, so existed as part of a far smaller sheltered gene pool.

I posted this because I have always wondered what the answer to this question was, but could not do the maths - it is very hard and can only really be done by simulation as Bob as done.

I suspect that the 46,000 genetic segments is an approximation, but it should not mess up the calculations too much if this is wrong. The truly amazing thing is how few real ancestors you have out of the possible number.

I highly recommend using an existing DNA service (I use FTDNA) to sequence the Y chromo and/or MTDNA of your living direct relatives (where it makes sense.. only one Y for male line, etc) because the samples are kept in storage and you can use them for sequencing later as technology drastically ramps up. My Y data is available to researchers and my and my father's MTDNA are in Genbank. Genetic anthropologists use the data to fine tune our knowledge of historical population movements. The current theory is that I am descendent from the Vistula Veneti. I just wish more people had an interest so that there were more data samples. You can't just go around demanding peoples' DNA, even if it has nothing to do with the parts that influence your health.