Worm Breeder's Gazette 8(2): 18

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.

Pachytene Karyotype Analysis of the rad-4 Radiation-Sensitive Mutant

P. Goldstein

Nuclear morphology at the pachytene stage of meiosis is altered in 
the rad-4 mutant such that the nuclei are 50% of the volume as that of 
wildtype.  In addition, the X:A ratio differs in rad-4 as compared 
with the wild-type.  Six synaptonemal complexes (SC), consisting of 
two lateral elements and a central element, are present in the 
pachytene nuclei of the C.  elegans hermaphrodites.  The XX bivalent 
pairs synchronously with the autosomes.  Three specific chromosomes 
can be identified out of the total of six: 1) The XX bivalent, SC#1, 
is the shortest; 2) the longest bivalent, SC#6, carries the nucleolar 
organizer region at the extreme end; and 3) the SC#5 has two 
'Disjunction Regulator Regions' (DRR) located approximately one  m 
apart from each other.  These DRRs either promote disjunction or 
inhibit nondisjunction of the X chromosome.  The decrease in the rate 
of X chromosome nondisjunction in this mutant is not related to the 
structure of the SC, but may be related to the number of DRRs, 
specifically it is observed in the rad-4 mutant that the DRRs occur 
with a higher frequency than in wild-type.  Other SC associated 
structures, such as recombination nodules, have not been observed in 
this strain or any other strain of C.  elegans.