Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!boulder!pell From: pell@boulder.Colorado.EDU (Anthony Pelletier) Newsgroups: sci.bio Subject: Re: embryology. A mini tutorial Message-ID: <8284@boulder.Colorado.EDU> Date: 21 Apr 89 21:39:57 GMT References: <3229@imagen.UUCP> <169@ascom.UUCP> <1957@trantor.harris-atd.com> Sender: news@boulder.Colorado.EDU Reply-To: pell@boulder.Colorado.EDU (Anthony Pelletier) Organization: University of Colorado, Boulder Lines: 23 In article hnewstrom@x102a.harris-atd.com (Harvey Newstrom) writes: > >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. Well...ummmm, I guess this is true if you consider fruit flies a "bird." Drosophila and C. elegans are the most common lab examples of sex being determined by the "X to A ratio." That is, 1X/2A=male (with or without Y)2X (or more)/2A=female. Intermediate ratios can give rise to intersexes. Now, an ornathologist I am not, but isn't it true that the sex chromosomes in birds are call W and Z? The difference, as I recall, is that the *female* is the heterogametic sex (W Z) and the male is the homogametic sex (W W, I think). > >Sometimes humans can be mottled, with a combination of different cells! This Mosaic: see David Bowie (I do, every chance I get) -tony