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Archiver > GENEALOGY-DNA > 2010-02 > 1265914819


From: Robert Stafford <>
Subject: Re: [DNA] Variance Assessment wrt back and parallel mutations
Date: Thu, 11 Feb 2010 13:00:19 -0600
References: <e0d2d2871002102020y511698demc1a7fb05516e5b89@mail.gmail.com>
In-Reply-To: <e0d2d2871002102020y511698demc1a7fb05516e5b89@mail.gmail.com>


The chances of having at least one parallel mutation are pretty good when
testing even a modest number of people with an ancestor 200-400 years ago.
We have tested 31 people descended from an ancestor first found in VA
records in 1682. We have 2 parallel mutations (DYS390 and DYS439) which were
verified by testing other branches. We also have another one (DYS459) for
which it is highly improbable that they shared a common ancestor within the
time frames when the mutations could have occurred.

We had lengthly discussions about parallel mutations on the list several
years ago. People do not have an intuitive grasp of coincidence
probabilities, as answers to the birthday paradox show. See this for a
discussion:

http://en.wikipedia.org/wiki/Birthday_problem

Using this calculation for FTDNA's 37 markers, there is about a 50:50 chance
of having one or more parallel mutations when you have 10 mutations.

Bob Stafford


On Wed, Feb 10, 2010 at 10:20 PM, David Ewing <>wrote:

> What I need help understanding is why I cannot make our data
> square with the expectation that back and parallel mutations should not be
> a significant factor in relatively shallow lineages.
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