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Archiver > GENEALOGY-DNA > 2002-10 > 1034025840


From: "John F. Chandler" <>
Subject: Re: [DNA] Mutations
Date: Mon, 7 Oct 2002 17:24 EDT
In-Reply-To: garyrea@cox.net message <004701c26cec$ffd620a0$1a466144@ok.cox.net> of Sat, 5 Oct 2002 22:01:10 -0600


Gary wrote:
> John, isn't the change of a particular marker that repeats twice a useful
> means of determining the time between events? For example, Bennett Greenspan
> (of FTDNA) has told me that my match, by two step mutations, to someone in
> the FTDNA database having Russian ancestry probably means our MRCA lived
> "many thousands of years ago," to quote Greenspan.

This is an example that shows the need for precise wording. I cannot
tell from the above whether your phrase "two step mutations" means
"two one-step mutations" or "[some] two-step mutations". The opening
remark about a *particular* marker that "repeats twice" suggests the
latter interpretation, and Bennett's statement about the MRCA also
suggests multiple mutations, but I happen to know that the FTDNA REO
interface doesn't list matches further removed than two steps total.
As such, bear in mind that the expected time to the MRCA is about 500
years per step for a 12-marker test.

> It's my understanding that mutations, although they can occur at
> any point along the timeline, usually occur at a rate of roughly every one
> thousand or so years.

There's no "usual" about it. They can and do occur at any point in time.
For a set of 12 markers, they occur at an AVERAGE rate of about one every
thousand years in a given line of descent. Obviously, when comparing
two lines, the combined AVERAGE rate is about one every 500 years.

John Chandler


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