Comments on: How Many Ancestors Share Our DNA?

By: Luke

Luke — Sun, 22 Jan 2012 22:30:33 +0000

@John Lloyd Scharf

We have about 3.08 billion base pairs. Therefore, we have about 6.16 billion bases and over 30 generations before we have to make a choice between one ancestor and another, one allele and another, at a particular base pair.

No that’s not how it works. You don’t have 3.08bn independent base pairs, you have 22 independent autosomes, the bases within which have a correlation structure dependent on recombination.

By: John Lloyd Scharf

John Lloyd Scharf — Sun, 22 Jan 2012 21:01:26 +0000

We have about 3.08 billion base pairs. Therefore, we have about 6.16 billion bases and over 30 generations before we have to make a choice between one ancestor and another, one allele and another, at a particular base pair.

About 30 generations at about 30 years per generation is about 900 years. 900 years ago our world population was between 310 million and 790 million. It is likely no more than 2/3rds of those have descendents to the present, given the effect of the plagues that happened between 900 years ago and now.

Without inbreeding, however, at 30 generations you have 1,073,741,824 ancestors. If the whole world were in your ancestry, then you would still have many cases of “inbreeding” with sixth cousins, seven times removed.

However, even if there were only 30 ethnic groups in relative reproductive isolation from each other, until the last 200 years there has been very little genetic sharing between groups. There was not much interbreeding, for instance, between native Americans and Mongolians 200 years ago. Genealogical ancestry does not extend much beyond 400 years ago.

Therefore, we can say that your genetic ancestors and your genealogical ancestors are in the same set and equivalent.

By: Aaron

Aaron — Tue, 06 Dec 2011 00:00:23 +0000

This information really revolutionizes our thinking about our ancestors, and it has been fun to study what you have done with this simulation.

It is known that recombination is not equal across the genome, and there are known recombination hotspots. It would be interesting to see how this analysis would look if you incorporated recombination rates across the genome. All of the data is accessible from HapMap’s website http://hapmap.ncbi.nlm.nih.gov/downloads/recombination/latest/rates/

Also, it is strange to me that you see such a leveling off in number of ancestors at 125, it even looks like the number of ancestors drops a little at 15 generations. Does your code include a minimum threshold for being identified as a relative? Otherwise, I don’t think that is possible.

Nice work, I hope you could generate a simulation with the recombination rate data, because it is way out of my league to try something like that.

By: Carlos

Carlos — Mon, 03 Oct 2011 18:38:42 +0000

Does it mean that ethnic affinities derived from autosomal DNA data are also that recent? (10-12 generations)

By: J C

J C — Tue, 13 Sep 2011 03:38:05 +0000

You are showing a point estimate but it would be nice to see the range of values. Can you repost the plots with 95% prediction intervals?

By: Using Genome-Wide SNP Scans to Explore Your Genetic Heritage

Using Genome-Wide SNP Scans to Explore Your Genetic Heritage — Wed, 04 Aug 2010 18:55:45 +0000

[...] Jostins at Genetic Inference kindly looked into my questions and offered some helpful and creative insight. Using a statistical [...]

By: Pamela Rowe

Pamela Rowe — Sun, 10 Jan 2010 20:15:16 +0000

I am a female and more closely related to my paternal line, 53.13%, according to Relative Finder. Almost everyone of my matches comes from my father’s side.
Some of his relatives, I am even more related to because of the recombination. On the average, it looks as though I may lose a few cm’s with most; although, many of our matches have remained exactly the same.
One particular high/distant cousin match for him, totally disappears for me.
All very interesting!

By: Leigh

Leigh — Tue, 24 Nov 2009 22:16:52 +0000

Was pleased to read about girls being closer to the maternal line. . .

By: E

Mon, 16 Nov 2009 16:10:03 +0000

“….you are, on average, slightly more closely related to your maternal line (your maternal grandmother, your mother’s maternal grandmother, etc) than you are to you paternal line (your father’s paternal grandfather, etc).”

Cool.

But, aren’t most people going to be more like their fathers, then, than their mothers since they should inherit more directly *groups* or *packages* of genes that did not recombine (i.e. that remain linked)?

By: Richard T

Richard T — Sun, 15 Nov 2009 06:36:45 +0000

Doh, can you tell it has been a while since my last genetics class? I guess the answer to my question above (which describes the situation of many 23andMe /DecodeMe customers) basically comes directly from the definition of a centimorgan. Feel free to delete the question.