Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucsd!sdcsvax!trantor.harris-atd.com!x102a!hnewstrom From: hnewstrom@x102a.harris-atd.com (Harvey Newstrom) Newsgroups: sci.bio Subject: Re: embryology. A mini tutorial Message-ID: <1957@trantor.harris-atd.com> Date: 21 Apr 89 17:08:59 GMT References: <3229@imagen.UUCP> <169@ascom.UUCP> Sender: news@trantor.harris-atd.com Reply-To: hnewstrom@x102a.harris-atd.com (Harvey Newstrom) Organization: Harris Corp, Govt Systems Sector, Info Systems, Software Lines: 21 In article <169@ascom.UUCP> rene@ascom.UUCP (Rene Bach) writes: >[....] >The only pair of chromosomes that look different is the SEX chromosome pair. >XY = males and XX for females (valid in many species but I believe not ALL). > >Rene Bach >Switzerland Obviously only valid for sexual (not asexual) creatures. 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. In some species, such as [some?] birds, it is the two X choromosomes which produce females, while their lack produces males. Thus, XXY is female, as is XXX. XO is male in these species. Sometimes humans can be mottled, with a combination of different cells! This is caused by two cells in the beginning merging into one fetus instead of forming twins!