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Archiver > GENEALOGY-DNA > 2007-07 > 1184643413


From: (John Chandler)
Subject: Re: [DNA] Bottlenecks - R1b1c7 as acalibration tool-The"final"version
Date: Mon, 16 Jul 2007 23:36:53 -0400 (EDT)
References: <3b2a446a0707141130q183c4272idd907eb9ca1457d1@mail.gmail.com><KHEKIJEABJGJEKDPFEDMMEFCDPAA.Elizabethod@eircom.net><3b2a446a0707141419l6ef9bcc0oe8ccb84af2c98763@mail.gmail.com><REME20070714192227@alum.mit.edu><3b2a446a0707161458s25350266icc24c08b01d83f2e@mail.gmail.com><00a901c7c7fe$a9ef6e90$0201a8c0@Masterbedroom><3b2a446a0707161744h43f2ce1agd928af4ca37ffadf@mail.gmail.com>
In-Reply-To: <3b2a446a0707161744h43f2ce1agd928af4ca37ffadf@mail.gmail.com>(sasson.margaliot@gmail.com)


Sasson wrote:
> What if for ten generations every man has on average three sons.
> At the end of ten generations the panel of experts is asked to estimate time
> to MRCA.

If every man has exactly three sons, it is easy to calculate the mean
TMRCA for the final population: it comes to 9.5 generations. More
generally, if the duration is G generations, and the population growth
rate is r per generation (i.e., r=2 in this case), we get a mean TMRCA
of G - [1 - (1+r)^(-G)]/r.

> The researchers assume realistic rate of population growth, not knowing that
> the actual rate was much higher. Would they estimate TMRCA as at least 50
> generations ?
>
> This is example where the "fudge factor" seems to be less than 1.

No, this example has an expected fudge factor of 1.05.

> My question was - is it the case that population expansion cannot contribute
> to lowering the fudge factor?

Population expansion can bring the fudge factor closer to unity, but
it cannot lower the fudge factor below unity. If you want to go
there, you need to rely on a highly improbable combination of
more-than-average mutations in the population you're studying.

John Chandler

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