Worm Breeder's Gazette 7(1): 84

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.

Nondisjunction and Knobby Chromosomes

P. Goldstein

Why don't chromosomes at meiotic prophase fall apart (or undergo 
disjunction) when they are supposed to?  Part of the answer lies in 
peculiar knobs attached to the synaptonemal complexes (SC) in C.   
elegans hermaphrodites and males.  It has recently been reported that 
these 'SC knobs' may represent active regions of DNA, as opposed to 
the more compact chromatin usually found at pachytene (Goldstein and 
Slatan, 1981).  Also, the number and distribution of these SCKs vary, 
such that the wild-type hermaphrodite has 6 SCKs (and shows 0.01% 
nondisjunction) while the him8 mutant (with 37% nondisjunction) has no 
such knobs (Goldstein, 1981).  The him4 mutant, which shows 16% 
nondisjunction and represents an intermediate situation, has 3 SCKs.  
Thus, it was suggested that the presence or absence of SCKs may 
mediate the nondisjunction process, such that the product of the 
active DNA region inhibits nondisjunction if present (6 SCKs in wild-
type-0.01%) and if this product is not present, then nondisjunction 
occurs (no SCKs in him8, 37% nondisjunction).  Recently, further 
evidence has been obtained to support this theory.  There are two SCKs 
in wild-type young males (4 days) this represents a true sex-
difference) however, in older males (7-9 days) no such SCKs are 
present.  The report by Rose and Baillie (1979) that nondisjunction 
increases with age (as revealed by increase in male progeny) 
correlates with the absence of SCKs in older males.