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Archiver > GENEALOGY-DNA > 2002-04 > 1018637178


From: (Ellen Keyne Seebacher)
Subject: RE: [DNA] Testing Australian parents' DNA + 'other' genetic material
Date: Fri, 12 Apr 2002 14:46:27 -0400 (EDT)
In-Reply-To: <01C1E21E.1BA3CB20.mmay@richmark.com>


> I believe it is correct that the X chromosome is a "nuclear"
> chromosome in women.

Yes, of course. I apologize if that wasn't clear.

> The X one gets from one's mother is not identical to either of the
> two X's she inherited, one from each parent, but is a combination of
> the two.

Not identical, true, but not really a combination either -- X chromosomes
recombine only in a very small area at their tips.

> Otherwise, we could trace genealogy with an X chromosome test, since
> it would be unchanging over time, with a 50-50 chance of being
> passed on to a child by a mother and a 100% chance to a female child
> by the father.

How could you trace it, if you didn't know which line it had been passed
along? Saying that your X chromosome arrived unchanged (which it hasn't,
of course; there is a _small_ amount of recombination, and there are
always mutation events) from an ancestor 10 generations ago doesn't help
if you don't know which of the 2^10 ancestors in that generation it might
have come from. And we women, who have two X chromosomes, would have
twice the confusion. :-)

--
Ellen Keyne Seebacher


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