Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/5/84; site reed.UUCP
Path: utzoo!linus!decvax!tektronix!reed!alexis
From: alexis@reed.UUCP (Alexis Dimitriadis)
Newsgroups: net.bio
Subject: Re: Human Genetics (a query)
Message-ID: <1775@reed.UUCP>
Date: Sun, 4-Aug-85 23:00:01 EDT
Article-I.D.: reed.1775
Posted: Sun Aug  4 23:00:01 1985
Date-Received: Wed, 7-Aug-85 01:29:06 EDT
References: <241@weitek.UUCP>
Reply-To: alexis@reed.UUCP (Alexis Dimitriadis)
Organization: Reed College, Portland, Oregon
Lines: 43
Summary: 

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?

  I believe they don't.  Recombination occurs between _homologous_
chromosomes, that is, chromosomes that are part of a "pair", and carry
genes for the same traits.  The X and Y chromosomes are completely
different chromosomes.  They do not pair up during meiosis, and thus no
recombination events take place.  It is a good thing they don't,
because any recombination of parts that are not equivalent would almost
certainly make the chromosome useless.  (Imagine trading _part_of_ your
gene for hemoglobin for part of a gene for eye color!)

The Y chromosome is a very unusual chromosome:  It is very
small, and as far as anybody knows it has (almost) no identifiable
genes on it.  It is thought that the gene for having a hairy 
pinnae (sp), (part of the earlobe), may be on the Y chromosome, and
one or two even odder things, but apart from those it does not
code for any phenotypic characteristics.  All the "sex linked" 
characters that you hear about in Biology class are on the X chromosome.

> 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.

  Note that as I implied above, recombination happens between arbitrary 
stretches of DNA, not in units of whole genes. A "sex gene" would not
be resistant to recombination.  At any rate, sex seems to be determined 
by regulatory mechanisms much more subtle than the possession of a 
particular gene.  Remember, men carry all the genes that women carry.

Alexis Dimitriadis
-- 
_______________________________________________
  As soon as I get a full time job, the opinions expressed above
will attach themselves to my employer, who will never be rid of
them again.

             alexis @ reed

	         ...teneron! \
...seismo!ihnp4! - tektronix! - reed.UUCP
     ...decvax! /