Path: utzoo!yunexus!maccs!cs4l3az
From: cs4l3az@maccs.UUCP (....Jose)
Newsgroups: sci.bio
Subject: RE: Sex Ratios
Message-ID: <1108@maccs.UUCP>
Date: 3 Apr 88 21:43:11 GMT
Article-I.D.: maccs.1108
Posted: Sun Apr  3 17:43:11 1988
Reply-To: cs4l3az@maccs.UUCP (....Jose)
Organization: McMaster University, Hamilton, Ontario
Lines: 28

In article <1988Mar31.124839.9957@utzoo.uucp> rising@utzoo.uucp (Jim Rising) writes:
>>Higher early (pre-natal; juvenile) mortality may be due to 
>>deleterious recessives on the X--for which the males are "homozygous."
>
>Mammals accomplish dosage compensation by completely shutting off one X.


	Actually, the "shutting off" of the X chromosome isn't of such 
importance... approximatley half of the female's body cells
will have the maternal X chromosome inactivated, the other
half having the fraternal X inactivated; thus any cell products 
which cannot be supplied by one set of cells can be supplied by another.
Also, those genes located on the tips of the X chromosome are not even
deactivated to begin with. 
	The genetic basis of the approximately 1:1 male:female sex ratios
is still not fully understood and is the subject of intense study;  that
the answer lies simply in how fast the sperm swim, or the vaginal pH
is unlikely.  (The vaginal pH DOES affect fertilization, apparently
by way of differences in antigens found on the surfaces of X sperm and 
Y sperm).


 
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"Fighting for Truth, Justice                         ....Jose Hachezero
and whatever might seem like                 Department of Biochemistry     
fun at the time"                                          cs4l3az@maccs
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