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.

Some Properties of Two New X Duplications

B. Herman, C. Kari, and M. Winter

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.