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.
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.