GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2010-03 > 1269889997


From: "RICHARD KENYON" <>
Subject: Re: [DNA] Family Finder Test
Date: Mon, 29 Mar 2010 12:19:06 -0700
References: <C03DB1E5-A1C7-440F-87D9-43BD49DFFD15@earthlink.net><2ea1ace51003290924n217da8a1x5acf09e075e9679a@mail.gmail.com><REME20100329143822@alum.mit.edu>
In-Reply-To: <C03DB1E5-A1C7-440F-87D9-43BD49DFFD15@earthlink.net><2ea1ace51003290924n217da8a1x5acf09e075e9679a@mail.gmail.com><REME20100329143822@alum.mit.edu>


Isn't this assuming a double crossover between an autosome pair? I would imply from examples I've seen in genetics texts on constructing linkage maps that single crossovers are much more likely, i.e. a single chiasmata rather than multiple chiasmata. I really don't know how to attack this quantitatively.

Richard R. Kenyon ("Dick")
----- Original Message -----
From: John Chandler<mailto:>
To: <mailto:>
Sent: Monday, March 29, 2010 11:45 AM
Subject: Re: [DNA] Family Finder Test


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

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