Archiver > GENEALOGY-DNA > 2010-03 > 1268942566

From: Nancy Kiser <>
Subject: Re: [DNA] Expected NPE's Over 800-1000 Years
Date: Thu, 18 Mar 2010 13:02:46 -0700 (PDT)
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In-Reply-To: <>

Hi, Lindsey,
The probability that a living male will carry the Y-signature of his surname’s progenitor from n generations ago is (1-p)n, where p is the fractional probability of a non-paternal event at each generation.  So first you have to decide what rate of NPEs per generation you think is reasonable and then you have to decide how many years constitute a generation.  I have read where some experts think 2% to 3% per generation is a reasonable estimate of NPEs and many experts use 25 to 30 years to calculate a generation.
If you use 30 years per generation, 800 years equals 26.67 generations and 1000 years equals 33.33 generations.  If you use 2% per generation as the average rate of NPEs, this suggests at the 25 generations 60% of the descendants of the progenitor will carry his Y-DNA signature and 40% will not.  At the end of 35 generations, 49% of the descendants of the progenitor will carry his Y-DNA signature, and 51% will not.
Hope this helps.
Nancy Kiser

----- Original Message ----
From: "" <>
Sent: Thu, March 18, 2010 12:37:02 PM
Subject: [DNA] Expected NPE's Over 800-1000 Years

We have 22  Britton families in our project.  One is known  to be the
result of a recent NPE and another may be the result of an 18th  century NPE.

I think I've seen estimates somewhere about the number of NPE's likely  to
occur over a certain period of time and am wondering whether  there is  any
method I can use to estimate how many of these 21 lines are likely to be 
NPE's and how many are likely to have used the name Britton since surnames
were  adopted.

At present only one line (mine) goes back to a known 17th century ancestor 
and we have tested lines of descent from two of his sons, but another line 
probably goes back at least that far, a third goes back to the mid-18th
century,  and a couple of others go back to c 1800.


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