Worm Breeder's Gazette 14(5): 21 (February 1, 1997)

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.

New Balancers for LG II

Mark L. Edgley, Carolyn Turner, Donald L. Riddle

110 Tucker Hall University of Missouri Columbia, MO 65211

We have been screening for new genetic balancers for the left arm of
chromosome II as part of the C. elegans Genetic Toolkit Project, in
cooperation with the Rose and Baillie laboratories.  We seek to isolate
rearrangements that balance to the left of dpy-10, perhaps extending to
the end of the chromosome.  The existing rearrangement mnC1 balances
well from the right end of the chromosome to just left of dpy-10.  The
semidominant mutation dpy-25(e817) has been used successfully to isolate
deficiencies in a relatively small region (Chen et al., Science 256:
240-243, 1992), but we wanted a balancer for generating overlapping
deficiencies across the entire left arm.

Irradiated dpy-10(e128) + / + unc-104(e1265) males were crossed with
unc-85(e1414) rol-1(e91) hermaphrodites.  Wild-type F1 cross progeny
were isolated and the F2 screened for the absence of Rol-1 non-Unc-85
recombinant animals, indicating suppression of recombination.  These
screens yielded four balancers (mC4, mC5, mC6 and mC7) in 2048
mutagenized chromosomes, all marked with dpy-10.  One of the balancers,
mC6, has been found to balance well from rol-1 leftward to let-552, but
balancing activity is reduced sharply between let-552 and sqt-2. 
Initial characterization shows mC6 to be homozygous-viable, and it is
probably an intrachromosomal rearrangement.  It is stable in crosses and
reduces recombination frequency by roughly 98% across the balanced
interval.  We are using it now to isolate deficiencies in the balanced

The remaining three balancers do not seem particularly useful to us for
isolating deficiencies, since they don't suppress recombination
adequately in the region of interest, but two of them are interesting
for other reasons.  mC7 may be a translocation, as it has relatively
small broods and segregates large numbers of dead eggs.  Homozygous mC7
animals are segregated at low frequency, and are invariably sterile.  We
have found that it balances rol-1 quite well (so far), but does not
balance unc-85 at all.  mC5 suppresses recombination between unc-85 and
rol-1, but not nearly as well as mC6, and it alters segregation ratios. 
Balancer homozygotes account for 31% to 34% of the progeny from an mC5
heterozygote, while animals homozyous for the balanced chromosome, which
was never subjected to mutagenesis, account for only 7% to 10%.  We see
this in both the original isolate (mC5/unc-85 rol-1) and in a
constructed stock (mC5/unc-104 rol-1).