How many genetic ancestors do you have?(burtleburtle.net)

46 pointsby danieltillett12년 전9 comments

http://burtleburtle.net/bob/future/ancestors.html

10 comments

> 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.

maxerickson12년 전

At the bottom, it says You had a trillion genealogical ancestors 40 generations back, which far exceeds the total number of people who have ever existed, so most of your ancestors appear many many times in your genealogical tree.

The links in my other comment talk a bit about measured genetic similarity (which should imply relatedness), it turns out there is a lot of mixing.

Sharlin12년 전

Yeah, it's pretty weird the author did not acknowledge this, especially seeing that the "Genealogical ancestors" column in the table is clearly nonsensical (nonillion ancestors?!)

danieltillett12년 전

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.

maxerickson12년 전

I posted one of the articles linked in this article a while back (without much discussion). The author did stop by and post a link to this article, which talks a little more about the consequences:

http://phenomena.nationalgeographic.com/2013/05/07/charlemag...

and this paper, which uses DNA analysis to look at ancestry in Europe:

http://www.plosbiology.org/article/info:doi/10.1371/journal....

vsbuffalo12년 전

Here's the thread if anyone is interested: https://news.ycombinator.com/item?id=7539143

apaprocki12년 전

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.

thaumasiotes12년 전

Out of two stylized models of the world:

    1. Every part of your DNA influences your health

    2. There is an identified portion of the human genetic code
       (including mtDNA) which has no effect on health

you'd have to be crazy to believe in model #2.

danieltillett12년 전

You can if they have been arrested. We are very close to entering an era where everyone will be able to know who they are related to and who they are not.

[deleted]12년 전