Worm Breeder's Gazette 8(3): 26

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.

Trisomy For Linkage Group IV

R. Herman, C. Horton, C. Kari

We described some of the properties of an X-IV fusion chromosome, 
called mnT12(IV;X), in an earlier Newsletter (Vol.  8, No.  1).  One 
characteristic we noted is that hermaphrodites homozygous for mnT12 
show high frequency meiotic nondisjunction of mnT12 and the normal X 
chromosome.  We have more recently shown that hermaphrodites 
heterozygous for mnT12 also show high frequency nondisjunction of 
mnT12 and the normal chromosome IV.  As a consequence they generate 
self progeny of chromosome composition IV/IV/mnT12/X.  The latter 
animals have essentially three copies of chromosome IV (and are also 
Him), since mnT12 has all of the essential genes of both IV and X.  
The phenotype of these animals is wild type, in contrast to the dumpy 
phenotype of triplo-X animals (Hodgkin et al.  1979).  We shall not 
describe here our evidence for the existence of IV/IV/mnT12/X animals. 
Instead, we shall describe our evidence for the existence of animals 
trisomic for normal linkage group IV only, which we were prompted by 
the mnT12 results (and Bob Horvitz) to construct.
Males of genotype unc-30 re crossed with 
him-6 dpy-4 IV/him-6 unc-22 
phrodites.  The three markers unc-22, 
situated in a 4 map unit segment 
and thus tend to balance each other.  The role of him-6 is to increase 
the frequency of diplo-IV ova through meiotic nondisjunction (Hodgkin 
et al.  1979).  Among 123 fertile wild-type progeny of the above cross,
two were trisomic for linkage group IV, as judged by progeny testing. 
These animals were unc-30 -6 
dpy-4/him-6 unc-30.  We have 
maintained a trisomic line by simply picking wild-type progeny and 
checking for the appearance of appropriate offspring.  The trisomics 
segregate principally seven phenotypic classes of self progeny.  These 
classes include (with their frequencies in parentheses; 707 total 
animals counted): wild type (0.25), Unc-22 (0.22), Unc-30 (0.15), Dpy (
0.20), Dpy Unc-22 nd 
Dpy  We have confirmed the presence of an 
extra chromosome by cytological inspection of oocytes.  The animals 
have small broods (about 150) but seem to be largely indistinguishable 
from wild type diploids under the dissecting microscope.