Worm Breeder's Gazette 9(2): 87
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
The new duplication mnDp63 carries the wild-type alleles of unc-1 and che-2, which are tightly-linked markers situated near the left-end of the X map. The duplication does not carry the nearby markers dpy-3 or unc-20 and it appears, cytologically, to be free (although larger than expected). The most surprising property of mnDp63 is the extremely high frequency at which it recombines with the X chromosome; in order to maintain a duplication stock, we must continually backcross unc-1(e538)/0;mnDp63 males with unc-1(e538) hermaphrodites. The duplication-bearing males are quite fertile and they produce the expected four sperm genotypes involving the presence or absence of X chromosome or duplication, but, in addition, roughly 17% of the X chromosomes carried by sperm are unc-1(+). This was shown by mating N2 males to individual wild-type hermaphrodites issuing from the cross of unc-1/0;mnDp63 males and unc-1;dpy-3 hermaphrodites and counting the male progeny. One of two very different patterns is found for each hermaphrodite. Hermaphrodite zygotes that derive from unc-1; mnDp63 sperm give many wild-type, uncdpy, unc and dpy male cross progeny. Hermaphrodite zygotes that derive from unc-1(+) sperm, however, give mostly wild-type and dpy-unc males; the few unc males and dpy males correspond to the incidence of recombinant types expected for the usual map distance between unc-1 and dpy-3 (about four map units), as if the unc-1(+) picked up from mnDp63 now resides at or near the normal unc-1 chromosomal locus. The unc-1(+) gene is somewhat unstably integrated, however: it is lost, with reversion to the unc-1 phenotype, at a frequency of roughly 10+E-3 per chromosome. We are interested in the further characterization of mnDp63, but, we are also interested in obtaining new free duplications of this region of the X chromosome to see if the high recombination is a property of the region, rather than some special characteristic of mnDp63.A severe constraint in the analysis of genetic mosaics produced by the somatic loss of free duplications has been the fact that suitable duplications are not yet available for much of the genome. In addition, it is often necessary to have, closely linked to the gene to be analyzed, one or more other genes whose cell-specific expressions have already been worked out, so that one can select or identify mosaic animals in which the duplication has been lost at particular places in the cell lineage. An alternative approach is to have a free duplication carrying an efficient amber suppressor. One can then, in principle, study the mosaic expression of any gene for which one has an allele that is well suppressed by a single copy of the amber suppressor. We recently identified what we believe is such a duplication, although we have not yet used it for mosaic analysis. The duplication was derived by EMS mutagenesis of the following stock: unc-13(e450); stDf1 X; mnDp30(X;f). The deficiency stDf1 was identified by Waterston (1981) as a recessive lethal mutation that suppressed the cold-sensitive lethal phenotype of homozygous sup-7(st5) , an efficient amber suppressor. The duplication mnDp30 carries dpy-8( +) and also sup-7(+) as judged by Southern blot analysis, kindly performed for us by D. Moerman and R. Waterston, of a dpy-8 p30 stock. The unc-13(e450) mutation, when homozygous by itself, results in a severely uncoordinated phenotype. One copy of sup-7(st5) suppresses unc-13(e450) enough to give a mild uncoordination (Waterston, 1981). Among eight EMS-induced revertants of unc-13(e450); stDf1; found to have a suppressor mutation carried by the free duplication (at least some of the others were probably sup- 5 mutations). The degree of suppression seems to be roughly comparable to that of sup-7(st5). We presume that the mutation is a sup-7 allele; the duplication bearing the mutation is called mnDp43. In a stock of genotype unc-13(e450); flu-2; mnDp43, dpy progeny (lacking the duplication) are paralyzed, and non-dpy progeny (carrying the duplication) are only mildly uncoordinated. Our next step will be to identify suppressible alleles of loci that can be used to identify specific genetic mosaics.