Worm Breeder's Gazette 8(1): 7

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.

An X-IV Fusion Chromosome

D.C. Sigurdson, R.K. Herman

We have identified a dominant X-chromosome nondisjunction mutant 
that differs from those studied previously.  It has been shown by 
pseudolinkage results to be a translocation involving X and IV, which 
we call mnT12(IV;X).  The X breakpoint maps to the right of the right-
most marker known, let-6, and the IV breakpoint appears to be near the 
left end of IV, i.e., the translocation appears to be a fusion of the 
right end of X with the left end of IV.  Donna Albertson, at the MRC 
Laboratory of Molecular Biology, has looked at embryonic cells of 
mnT12 homozygotes and confirmed the existence of a fusion chromosome: 
she has taken nice pictures of cells showing 10 chromosomes in place 
of the normal 12, with one pair about twice as large as the normal 
pairs, which are roughly all the same size.  Assuming tips of X and IV 
have been lost, the losses must not have been extensive because mnT12 
homozygotes are viable and fertile.  Hermaphrodites heterozygous for 
mnT12 segregate about 27% males among their self progeny.  We have 
looked for nondisjunction of mnT12 and the normal IV in heterozygous 
males and have not detected it.  The heterozygous males also sire 
close to equal numbers of male and hermaphrodite progeny.  The mnT12 
homozygotes are non-Him, as expected, and appear to have little 
nondisjunction of the mnT12 chromosomes.  We are studying 
recombination between the two fusion chromosomes in the homozygote, 
and we are inquiring about the stability of the fusion.  Finally, it 
is worth noting that a line of C.  elegans can be maintained in which 
males have a neo-X (fusion chromosome) neo-Y (normal IV) genotype and 
hermaphrodites have two neo-X chromosomes and no neo-Y, i.e., the 
organism is converted from an XO type of sex determination to an XY