GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2010-03 > 1269888033


From: (John Chandler)
Subject: Re: [DNA] Family Finder Test
Date: Mon, 29 Mar 2010 14:45:51 -0400
References: <C03DB1E5-A1C7-440F-87D9-43BD49DFFD15@earthlink.net><2ea1ace51003290924n217da8a1x5acf09e075e9679a@mail.gmail.com>
In-Reply-To: <2ea1ace51003290924n217da8a1x5acf09e075e9679a@mail.gmail.com>(message from Stephen Forrest on Mon, 29 Mar 2010 12:24:30 -0400)


Stephen wrote:
> We know that the mean amount of nuclear DNA shared between two full siblings
> is 50% of the total. What is the variance?

This question has come up before. You can get a quick answer by
assuming some uniform rate of recombination. For example, suppose
each autosome splits into three equal pieces and recombines at each
meiosis. There are then 132 independent units of inheritance, and the
mean number of shared units is 66, with a standard deviation of about
8. That gives a 95% confidence interval for the fraction of shared
DNA of about 0.4 to 0.6. The correct solution is much more
complicated, since the number and location of crossovers are both
variable, but the true answer can't be very different from the simple
one.

John Chandler


This thread: