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From: emigh@ecsvax.UUCP (Ted Emigh)
Newsgroups: net.bio
Subject: Re: Human Genetics (a query)
Message-ID: <241@ecsvax.UUCP>
Date: Tue, 13-Aug-85 10:52:56 EDT
Article-I.D.: ecsvax.241
Posted: Tue Aug 13 10:52:56 1985
Date-Received: Mon, 19-Aug-85 06:12:12 EDT
References: <241@weitek.UUCP> <1775@reed.UUCP> <186@cylixd.UUCP>
Reply-To: emigh@ecsvax.UUCP (Ted Emigh)
Organization: NC State University
Lines: 43


  Sorry about this reply, but I just returned from the Joint Statistical
Meetings and my office is being painted, so if I can't do anything productive
I might as well do something on the net.

  The mechanisms of sex determinism are not very well understood at the
present time.  What we do know is:
1)	Until 7 weeks of gestation, a fetus has both sets of sex structures
	(in primitive form).  At that time, individuals who are destined to
	become males will develop the male structures.  Somewhat later (a week
	or two), the rest will develop the female structures.

2)	After 12 weeks gestation, the sex of the fetus can be determined
	by visual inspection.

3)	This time from 7 to 12 weeks is a very critical period for the fetus,
	and they are very sensitive to external stimuli.  This is the time
	when all the thalidomide damage is done.  It is possible to interfere
	with the sex determinism at this time with various sex hormones (see
	work by Money at Johns Hopkins).

4)	The factor that "makes a male" is located on the Y chromosome (or,
	rather, the factor that starts the process).  It is thought that this
	gene is at the very tip of the Y chromosome, as there are XX males
	who have this small fragment of Y chromosome attached to a normal X
	chromosome.

5)	During meiosis, the X and Y chromosome will pair up to a certain
	extent.  No doubt, this is needed to assure that the proper number
	of chromosomes are in each daughter cell.  While autosomal chromosomes
	(not the sex ones) pair as =======, the X and Y will pair as
	-------v-- (X chromosome on the left, Y on the right in this diagram,
	with a very small area pairing).

I will be glad to expand on any of these.


-- 

Ted H. Emigh     Genetics and Statistics, North Carolina State U, Raleigh  NC
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