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From: mrh@cybvax0.UUCP (Mike Huybensz)
Newsgroups: sci.med
Subject: Re: sex and color
Message-ID: <1229@cybvax0.UUCP>
Date: Sun, 9-Nov-86 14:03:18 EST
Article-I.D.: cybvax0.1229
Posted: Sun Nov  9 14:03:18 1986
Date-Received: Wed, 12-Nov-86 10:18:48 EST
References: <2302@bucse.bu-cs.BU.EDU> <7858@tekecs.TEK.COM>
Reply-To: mrh@cybvax0.UUCP (Mike Huybensz)
Organization: Cybermation, Inc., Cambridge, MA
Lines: 18

In article <7858@tekecs.TEK.COM> mikes@tekecs.TEK.COM (Michael Sellers) writes:
> If I remember correctly, the second X chromosome in females sits unused in
> the nucleus (it never "unbundles" in interphase like the rest of the 
> chromosomes do).  These are called "Barr bodies", after the guy who 
> discovered them.  If my recollection is correct, then this would seem to 
> imply that females do not benefit from anything on the "extra" X chromosome.
> Can anyone closer to a genetics text confirm or deny my remembrance?

Yes, in each cell of a female human (sex determination methods of different
organisms vary quite a bit) all but one of the X chromosomes sit around
doing nothing as Barr bodies.  But not necessarily the same X chromosome in
each cell.  If that were the case, we'd see many recessive, sex-linked traits
that are carried on the X chromosome (such as color-blindness) occuring with
exactly half the frequency that they do in males.

So genes on both X chromosomes normally are expressed in women.
-- 

Mike Huybensz		...decvax!genrad!mit-eddie!cybvax0!mrh