Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!gatech!hao!boulder!eddy From: eddy@boulder.Colorado.EDU (Sean Eddy) Newsgroups: sci.bio Subject: Re: C. elegans Message-ID: <1067@sigi.Colorado.EDU> Date: Sat, 9-May-87 13:43:12 EDT Article-I.D.: sigi.1067 Posted: Sat May 9 13:43:12 1987 Date-Received: Sun, 10-May-87 05:17:00 EDT References: <1055@thebes.UUCP> <9576@duke.cs.duke.edu> <1640@zeus.TEK.COM> <1044@sigi.Colorado.EDU> <1055@aecom.YU.EDU> Sender: news@sigi.Colorado.EDU Reply-To: eddy@boulder.Colorado.EDU (Sean Eddy) Organization: University of Colorado, Boulder Lines: 55 In article <1055@aecom.YU.EDU> werner@aecom.YU.EDU (Craig Werner) writes: >> >In article <1640@zeus.TEK.COM>, dant@tekla.tek.com.tek.com (Dan Tilque;1893;92-789;LP=A;60/C) writes: >> >> >> is a legitimate exception; in fact, I would not call C. elegans >> reproduction parthenogenesis at all. > > C. elegans has two sexes. Hermaphrodites (which are both male >and female combined) and Males (which only produce sperm). Females are >XX, there is no Y chromosome, males are X (or XO signifying 1 X only), >and arise by a non-disjunction event. > > Sex determination arises in different ways. In C. elegans, it >is the X/autosome ratio. If one has half the number of X chromosomes >compared to everything else, one is a male, hermaphroditic otherwise. > In Drosophila, males are XY, females are XX, on the surface >the same as mammals, but XXY are female and XYY are male, so it is the >presence or absence of the second X that is important, Y is just a >place-holder. Firstly, having had my explanation on C. elegans written correctly by Craig, I apologize for being incomplete -- having just finished a 24 hour final that covered the subject, I was not psyched to write everything again. Secondly, Craig's explanation of sex determination in Drosophila is incomplete, and since I've now recovered from my final, I'll try to remember this stuff... Like C. elegans, sex determination in Drosophila is determined by the X/A ratio (X chromosomes to autosomal chromosomes). The Y chromosome of Drosophila has no role in sex determination. As this is a shocking statement to us mammals, I refer you to the 1983 Annual Review of Genetics, vol 17, p. 345; or to Bridges' original work in 1916, published in vol. 1 of Genetics, p. 1. It isn't the second X per se that determines the sex of the animal, it is how many X's there are compared to A's. Normal flies would be 2X/2A females and 1X/2A males. Bridges could make aneuploid flies (abnormal chromosome numbers); he found that 1X/1A flies were females even though they had only 1X. By determining the sexes of many such flies (3X/3A,4X/4A,3X/2A, etc.) Bridges concluded that an X/A ratio of 0.5 or lower made a male fly, a ratio of 1.0 or higher made a female fly, and intermediate ratios produced an intersexual phenotype. So it would appear that sex determination in C. elegans and Drosophila are, on the surface, actually similar. - Sean Eddy - Dept. of Molecular, Cellular, Developmental Biology - Univ. of Colorado, Boulder; Boulder, CO 80309 - - "You can't possibly be a scientist if you mind people thinking - that you're a fool." - -from So Long and Thanks for All the Fish