Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ncar!noao!asuvax!hrc!gtx!sue From: sue@gtx.com (Sue Miller) Newsgroups: sci.bio Subject: Re: embryology. A mini tutorial Message-ID: <965@gtx.com> Date: 23 Apr 89 22:24:13 GMT References: <3229@imagen.UUCP> <169@ascom.UUCP> <1957@trantor.harris-atd.com> Reply-To: sue@gtx.UUCP (Sue Miller) Organization: GTX Corporation, Phoenix, Arizona Lines: 29 In article <1957@trantor.harris-atd.com> hnewstrom@x102a.harris-atd.com (Harvey Newstrom) writes: > >In humans the Y chromosome produces males, while its lack produces females. >Thus, XXY is male, while XXX is female. XO is female, but I don't think any >survive in humans. XO is female, but they do survive in humans - the resulting abnormal condition is called Turner's syndrome. The phenotypic characteristics of Turner's syndrome are short stature, wide, web-like neck, poorly developed breasts, and immature internal sexual organs, and sometimes mental deficiency. I used to work with a woman whose daughter-in-law had Turner's syndrome - she was short, but not really "abnormal" in appearance (whatever that means). What surprises me a little is that many organisms are pretty tolerant about wide ranging variations in number/distribution of the sex chromosomes, but such variations are definitely NOT tolerated well in the autosomal pairs. Trisomy-21, familiar to all as Down syndrome, is the only common such aberration, and it involves a fair amt of impairment (depending on the individual, of course). My genetics textbook lists 2 other trisomic abnormalities, trisomy-13 (1/5000 births) and trisomy-18 (1/10000 births). It's my understanding that these 2 conditions have extremely high mortality rates, and surviving victims are quite severely handicapped. Warning - WAG follows: Can it be that there isn't such a big deal about our sex after all? :-) -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Sue Miller {decvax,hplabs,amdahl,nsc}!sun!sunburn!gtx!sue ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~