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Archiver > GENEALOGY-DNA > 2011-12 > 1322933415


From: Obed W Odom <>
Subject: Re: [DNA] D Faux's cousins
Date: Sat, 03 Dec 2011 11:30:15 -0600
References: <mailman.175.1322869475.20702.genealogy-dna@rootsweb.com><C943924D-B236-4D5B-8979-68F9EA2052B9@charter.net><4EDA4AD5.5000901@mail.utexas.edu>
In-Reply-To: <4EDA4AD5.5000901@mail.utexas.edu>


In my previous post (below) I think I overestimated the chance of *both*
siblings having no crossover on any of their 44 autosomes. The number I
gave, (1/2)exp44, was the chance of one of the siblings having no
crossover, so the chance of both siblings having no crossover would be
(1/2)exp88, making the odds of 2 siblings sharing zero segments
(1/2)exp132, or only 1 out of 5445 trillion trillion trillion.

On 12/3/2011 10:14 AM, Obed W Odom wrote:
> The odds of 2 true siblings sharing zero segments would certainly be
> less than (1/2)exp44, or 1 out of 17.6 trillion. This number assumes no
> crossing over between homologous chromosomes. If one assumes that for
> each autosomal chromosome pair there is a 50% chance of having no
> crossover, then the chance of having no crossover on *any* of the 44
> inherited autosomal chromosomes would again be (1/2)exp44, making the
> odds of 2 siblings sharing zero segments (1/2)exp88, or 1 out of 309
> trillion trillion, a truly vanishingly small number.
>


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