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Archiver > GENEALOGY-DNA > 2002-03 > 1017104520


From: "John F. Chandler" <>
Subject: Re: [DNA] Confidence in labs
Date: Mon, 25 Mar 2002 20:02 EST
In-Reply-To: agleason@route66web.com message <3C9FC31F.1B4A66E2@route66web.com> of Mon, 25 Mar 2002 17:39:33 -0700


Allan wrote:
> Lets be generous and say that with 12 markers with 4 coequal states there
> would be about 500 combinations.

I'm not sure where you got that result. The correct answer is 4 raised
to the 12th power, i.e., over 16 million combinations. Even if you
decide to be stingy and figure only 3 states for each marker, you still
get over half a million combinations. With 22 markers, these numbers
go up to 17 trillion and 31 billion in the same two "generous" and
"stingy" cases. (These are the American/French trillions, not the
British/German flavor.)

Don't forget that most people have an assortment of close male relatives
who would *expect* to be identical (barring non-paternity events). If
you start with yourself and work outward through brothers, sons, fathers,
and so on, you probably reach about 20 males before you run into the
first mutation in a 12-marker test. However, you can't stop there
because a certain fraction of your ever more distant cousins will still
come through with identical haplotypes. All told, if you consider the
descendants of your male-line ancestor back in 1600 and discount the
fecundity since 1900, you get perhaps 10,000 living male-line descendants
now, and perhaps 600 separate mutation events between then and now (most
of which would simply populate the 24 adjacent states). Since we are
being generous, lets figure the 10,000 males fall into 50 different
haplotypes by natural variation. That means you would expect to share
your 12-marker result with about 200 other directly related individuals
with the same surname. That would parlay the 16 million available
haplotypes into space for 3 billion living males, or 6 billion people
in all. What a coincidence!

The problem, of course, is that many of the possible states are empty,
while some states are heavily overpopulated.

John Chandler

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