Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!oli-stl!asylum!ayermish
From: ayermish@asylum.SF.CA.US (Aimee Yermish)
Newsgroups: sci.bio
Subject: Re: twins
Message-ID: <1091@asylum.SF.CA.US>
Date: 1 Feb 89 00:16:54 GMT
References: <1046@jimi.cs.unlv.edu> <775@bimacs.BITNET>
Reply-To: ayermish@asylum.UUCP (Aimee Yermish)
Organization: The Asylum; Belmont, CA
Lines: 18

Another very long shot on how you could get monozygotic twins to be of
different sexes:  If they both started out female, but right early on 
(I mean *really* early on, although I don't know enough about
developmental bio to say more specifically) one of them had a breakage
(or maybe a very lucky translocation) in one X chromosome cutting it
short such that it was for most intents and purposes a Y chromosome.
Of course, the chances that the break would happen in just the right
place are vanishingly small, leaving the poor kid with some gene
dosage screwups.

I *said* it was a very long shot...

--Aimee

-- 
Aimee Yermish				ayermish@asylum.sf.ca.us
Program in Cancer Biology		ayermish@portia.stanford.edu
Stanford University			415-594-9268