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From: charli@cylixd.UUCP (Charli Phillips)
Newsgroups: net.bio
Subject: Re: Human Genetics (a query)
Message-ID: <186@cylixd.UUCP>
Date: Thu, 8-Aug-85 20:59:12 EDT
Article-I.D.: cylixd.186
Posted: Thu Aug  8 20:59:12 1985
Date-Received: Mon, 12-Aug-85 07:15:56 EDT
References: <241@weitek.UUCP> <1775@reed.UUCP>
Reply-To: charli@cylixd.UUCP (Charli Phillips)
Organization: RCA-Cylix Communications Network Inc., Memphis, Tn.
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In article <241@weitek.UUCP> mmm@weitek.UUCP (Mark Thorson) writes:
> I have a question about biology that some netter should be able to
> answer:  Do human X and Y chromosomes recombine?

and

> But do the sex chromosomes recombine?  If they do, [...]
>		Sex would have to (?) be contained at one site
> so it would be resistant to splitting via recombination.

If I remember correctly from the Human Medical Genetic course I took
in college some years ago, the only known function of the Y chromosome
was to "turn on" the production of androgen at an early stage of
pre-natal development.  All fetuses develop as females before that
point, and those with a Y chromosome "become" males as a result of
the effects of the androgen.  Because some XY fetuses are insensitive
to the effects of androgen, it is possible for a genotypic male to be
a phenotypic female in every respect, including reproductive ability.
(Such XY women are typically infertile but not sterile, since their
"Y" eggs are useless.) Recombination of genes across the X and Y
chromosomes probably occurs for those few genes that are on the Y
chromosome, but it is an extremely small gene and seems to carry very 
little information.