eddy@boulder.UUCP (05/06/87)
In article <872@bgsuvax.UUCP> gagen@bgsuvax.UUCP (kathleen gagen) writes: >In article <1640@zeus.TEK.COM>, dant@tekla.tek.com.tek.com (Dan Tilque;1893;92-789;LP=A;60/C) writes: >> >> One aspect of parthenogenic reproduction which seems to be common in all >> of the species mentioned so far, is that the parthenogenisis seems to >> be stimulated by mating behavior or sperm from the males of a related > >I can think of at least two exceptions to this statment: >(1) In Cenorhabditis elegans (I hope that I spelled that right), parthenogenic >females do not require the presence of male stimulation to produce offspring. >(C. elegans is a self-fertilizing roundworm.) > >(2) The behavior of the artificially produced Drosophila strain "lazy girl" >is altered in that the "lazy girls" repell male advances. C. elegans is not female (except in some sex determination mutants). Instead, it is a hermaphrodite...C. elegans hermaphrodites produce both oocytes and sperm. I don't think, then, that C. elegans is a legitimate exception; in fact, I would not call C. elegans reproduction parthenogenesis at all. - 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
werner@aecom.YU.EDU (Craig Werner) (05/08/87)
In article <1044@sigi.Colorado.EDU>, eddy@boulder.Colorado.EDU (Sean Eddy) writes: > In article <872@bgsuvax.UUCP> gagen@bgsuvax.UUCP (kathleen gagen) writes: > >In article <1640@zeus.TEK.COM>, dant@tekla.tek.com.tek.com (Dan Tilque;1893;92-789;LP=A;60/C) writes: > >> > C. elegans is not female (except in some sex determination mutants). > Instead, it is a hermaphrodite...C. elegans hermaphrodites produce > both oocytes and sperm. I don't think, then, that C. elegans > 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. Most nematodes, on the other hand, have two definite sexes, where XX is female and X is male. 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. In birds, males have the identical chromosome, and it is females that are hemizygous. In mammals, it is of course, the case that the Y chromosome contains the signal for sex determination, or at least the primary signal. ~. -- Craig Werner (MD/PhD '91) !philabs!aecom!werner (1935-14E Eastchester Rd., Bronx NY 10461, 212-931-2517) "I refuse to do mental battle with an unarmed opponent."
eddy@boulder.Colorado.EDU (Sean Eddy) (05/09/87)
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
pell@boulder.Colorado.EDU (Anthony Pelletier) (05/13/87)
Distribution:sci.bio In article <1055@aecom.YU.EDU> werner@aecom.YU.EDU (Craig Werner) writes: > > 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. > Most nematodes, on the other hand, have two definite sexes, where >XX is female and X is male. > I must admit that I was tempted simply to take the advice of the quote at the bottom of your article to heart and not reply; but I decided that it might provide sufficient amusment to respond to your posting even at the risk of a prolonged discussion with a twit. If you choose to give an introductory lecture on on a topic, do try to get it right. Sean is quite competent and has already corrected a few of your errors. I will point out only one more. You are right that: C. elegans exist as male or hermaphrodite; the XX animals are hermaphrodite and the X_ animals are male; and males can arise in populations of hermaphrodites through a non-disjunction of the X during meiosis. You are incorrect in your statement that this differs from other nematodes, which are also male/hermaphrodite species in which the male is X_. In a cross fertilization between male and hermaphrodite C. elegans, the offspring are the expected 50% male. Meiosis and fertilization are not fundamentally different. You still get one X_ animal for each XX. The reason for the low frequency of males even inn mixed populations is that "The worm...prefers not to copulate at all with others but rather prefers itself... It is after all British" as John Sulstan so eloquently put it at the 1983 Cold Spring Harbor Symposium on Quantitative Biology (Neurobiology, that year). This species of nematode does have "two definite sexes" as do the others. The hermaphrodites simply prefer not to mate and do so only when cornered (it helps, if one wishes to do a cross, to make the hermaphrodite unco-ordinated by mutation, so that she cannot get away). One more thing, any tech who sub-clones something into pBR has a plasmid with her/his initials. We are not impressed. >~. > >-- > Craig Werner (MD/PhD '91) Craig, if you mean second year student, say second year student. A.J. Pelletier
werner@aecom.UUCP (05/15/87)
In article <1090@sigi.Colorado.EDU>, pell@boulder.Colorado.EDU (Anthony Pelletier) writes: > In article <1055@aecom.YU.EDU> werner@aecom.YU.EDU (Craig Werner) writes: > > > > Most nematodes, on the other hand, have two definite sexes, where > >XX is female and X is male. > > > non-disjunction of the X during meiosis. You are incorrect in your statement > that this differs from other nematodes, which are also male/hermaphrodite > species in which the male is X_. No, I was not incorrect in that statement. Most parasitic nematodes, if not all, have a male (which makes only sperm) and a female (which produces only ova), and this also holds for most free living nematodes as well (or so I have been repeatedly told by a variety of C. elegans workers). I only know that there are two sexes in all the filarial nematode species: Brugia malayi, B. pahangi, Wuchereria bancrofti, Onchocerca volvulus, Dirofilariae immitis, etc, etc... Now the big question. Does it really matter? -- Craig Werner (MD/PhD '91) !philabs!aecom!werner (1935-14E Eastchester Rd., Bronx NY 10461, 212-931-2517) "The DNA genetic system is the one library in which it is worthwhile to browse"
bill@dorrit.as.utexas.edu (06/27/91)
I just wanted to alert people to an interesting article on C. elegans in the latest _Science_ (v. 252, pp. 1619-20, 21 June 1991). Main points: A group at Washington University is well along in sequencing the entire genome (goal: done by the year 2000). Some interesting surprises. The 302-neuron nervous system of this organism shows some surprising capabilities to learn. C. elegans may be useful in constructing useful bioassays for toxicology, environmental contaminants, and other purposes. Bill Jefferys
tbd@neuro (Tristan Davies) (06/27/91)
In article <51261@ut-emx.uucp> bill@dorrit.as.utexas.edu writes: >I just wanted to alert people to an interesting >article on C. elegans in the latest _Science_ >(v. 252, pp. 1619-20, 21 June 1991). Main points: > > A group at Washington University is well along > in sequencing the entire genome (goal: done by > the year 2000). Some interesting surprises. > > The 302-neuron nervous system of this organism > shows some surprising capabilities to learn. > > C. elegans may be useful in constructing useful > bioassays for toxicology, environmental > contaminants, and other purposes. > >Bill Jefferys Actually, the effort to understand C. elegans has been underway since 1963, when Sydney Brenner (at the MRC in Cambridge, England) decided that with a small animal like C. elegans, it should be possible to unravel the details of its existence. One of the first areas to be expolored was the nervous system, which was painstakingly reconstructed in its entirety from serial electron microscopic sections (think about how difficult that was!!). The idea: if we can identify every neuron and the connections it makes, we should be able to understand how this nervous system guided the behavior of the animal, from input to output. So far, I'm not sure whether this has really happened. I imagine that behaviors aren't quite so easy to understand. Another valuable area of research on the C. elegans nervous system has been cell death. As far as I can tell, it was in C. elegans that researchers first realized that some cells are fated to die during the natural course of development. I imagine that the C. elegans genome project will run into some of the same problems as the above-mentioned nervous system reconstructions; just because you have all the pieces doesn't mean you can solve the puzzle. This project's success should also be interesting in rerlatiojn to the human genome project. If sequencing C. elegans' genome doesn`t lead to a complete understanding of that animal, how can we expect the human genome project to be very useful for understanding humans? FYI, a lot of the facts in this post come from another interesting article: "The Worm Project," Science vol. 248, p.1310, 15 June 1990. By the way, has there been much discussion of the human Genome Project in this group? If not, how about starting one? Happy trails! Tristan "don't ask me. I'm just a worm" Davies e-mail: tbd@neuro.duke.edu Department of Neurobiology, Duke University Medical Center grblb blabt unt mipt speeb!! oot piffoo blaboo..." -- Opus
ouellett@newsserver.sfu.ca (Francis Ouellette) (06/28/91)
In <22455@duke.cs.duke.edu> tbd@neuro (Tristan Davies) writes: >By the way, has there been much discussion of the human Genome Project >in this group? If not, how about starting one? This was already done on bionet.molbio.bio-matrix (or was it bionet.molbio.genome-program?) to some great extent just a few months ago. maybe the one done at this level (sci.bio) would reach a broader input ... it could be intersting! francis -- Francis Ouellette "Je cherche a` comprendre" Dept of Biological Sciences Jacques Monod Simon Fraser University ouellett@whistler.sfu.ca Burnaby, BC, Canada V5A 1S6 userBFFO@SFU.bitnet
cl@lgc.com (Cameron Laird) (06/28/91)
In article <22455@duke.cs.duke.edu> tbd@neuro.duke.edu (Tristan Davies) writes: . . . > Actually, the effort to understand C. elegans has been underway >since 1963, when Sydney Brenner (at the MRC in Cambridge, England) decided >that with a small animal like C. elegans, it should be possible to unravel >the details of its existence. One of the first areas to be expolored >was the nervous system, which was painstakingly reconstructed >in its entirety from serial electron microscopic sections (think . . . ... and a big part of the idea was to undertake this with an eye toward the developmental biology. The C. elegans workers not only have elucidated the wiring of the nervous system, but also how that nervous system grows within the individual, from its beginning as a single cell. The molecular biologists joined the party next, I think, so that now there are intensive efforts on structure and function at all (?) levels. -- Cameron Laird +1 713-579-4613 cl@lgc.com (cl%lgc.com@uunet.uu.net) +1 713-996-8546
tbd@neuro (Tristan Davies) (06/29/91)
In article <1991Jun28.130653.9301@lgc.com> cl@lgc.com (Cameron Laird) writes: > . >... and a big part of the idea was to undertake >this with an eye toward the developmental biology. >The C. elegans workers not only have elucidated >the wiring of the nervous system, but also how >that nervous system grows within the individual, >from its beginning as a single cell. The molecular >biologists joined the party next, I think, so that >now there are intensive efforts on structure and >function at all (?) levels. >-- Not to beat a dead horse (um, worm?), but... It strikes me that this "attack on all fronts" approach is much more likely to yield fruit than a "let's use high technology to study just one thing" approach, especially if everyone communicates with each other. That way, the cell biologists can ask the molecular biologists what might be causing a mutation or regulating a process, and the mol-biologists can concentrate their efforts in an area where results will be immediately useful. Again, I think this is what tends to happen in the research on C. elegans (as pointed out in the above quotation from Cameron Laird), which is why research on this animal continues unabated even though much of current research in neurobiology is moving towards vertebrates. Hmm...maybe this discussion should be continued in bionet.neuroscience? Cheers, Tristan "I wish *I* had 302 neurons!" Davies e-mail: tbd@neuro.duke.edu Department of Neurobiology, Duke University Medical Center "grblb blabt unt mipt speeb!! oot piffoo blaboo..." -- Opus