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Archiver > GENEALOGY-DNA > 2005-08 > 1123136673


From: "Lowe DNA" <>
Subject: RE: SMGF [was Re: [DNA] FTDNA Genetic Distance Calculations...]
Date: Thu, 4 Aug 2005 01:24:33 -0500
In-Reply-To: <REME20050803190044@alum.mit.edu>


John...

Glad that I asked about this "basic point" and hope the readers
here take note.

Never pay attention to the calculation procedure as a genealogist
just take it for granted that FTDNA has it down pat for me.

However, this is a good explanation and makes perfect sense.

Thanks

Bill

-----Original Message-----
From: John Chandler [mailto:]
Sent: Wednesday, August 03, 2005 6:04 PM
To:
Subject: Re: SMGF [was Re: [DNA] FTDNA Genetic Distance Calculations...]


I wrote:
> "For example, four one-step mismatches would give 21/25
> agreement and a genetic distance of 4, but four two-step mismatches
> would give the same 21/25 agreement and a genetic distance of 8."

Bill replied:
> You lost me completely on this one.??????

To be a little more explicit, suppose we are comparing two 25-marker
haplotypes, and 21 markers agree while 4 differ by one step each. We
would call this a 21/25 "match" (or "near-match"), and the genetic
distance is 4. In a second example, let's suppose that the same 4
markers differ by two steps each instead, while the other 21 markers
still agree. This is, therefore, still a 21/25 match, but the genetic
distance is now 8.

I realize that some people have fallen into the habit of subtracting
the genetic distance from the number of markers compared and, in the
second example above, would report the match as "17/25", but that
habit is entirely wrong (not to mention illogical). This is a basic
point that hasn't been discussed recently (because nobody has asked
any questions about this sort of notation recently -- until today).

John Chandler


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