Worm Breeder's Gazette 9(3): 45

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.

Lethal Alleles of "Visible" Genes

A.M. Howell and A.M. Rose

As part of our continuing analysis of essential genes on the left 
third of LG I, we have been testing our sDp2-rescued lethals for 
complementation with previously defined genes in the region. To our 
surprise, we have found lethal alleles of two genes which were not 
known to be essential genes. We have recovered an EMS-induced lethal 
allele of bli-4 and both EMS and gamma radiation-induced lethal 
alleles of him-l.The lethal allele of bli-4, h42, maps half way 
between dpy and unc-13. The phenotype of bli-4(e937)/bli-4(h42) is 
blistered, whereas bli-4 (h42) is a recessive lethal mutation. h42 
also fails to complement let-77 (s90) which maps to the left of dpy-14.
h42 may be a small deficiency of bli-4 and let-77, however, since we 
use a low dose of EMS (0.012 M), it is unlikely that h42 is a 
deficiency. It seems more likely that bli-4 and let-77 are really the 
same gene. Complementation between e937 and s90 is being done.
Both the EMS- (h134) and gamma-induced (h55) recessive lethal 
alleles of him-l map 0.5 map units to the left of (or above?) dpy-S, 
exactly where the original (and only) allele (e879) was mapped 
[Hodgkin, Horvitz and Brenner (1979) Genetics 91: 67-94]. The lethal 
alleles have a similar late larval or sterile adult phenotype. e879 
produces about 20% males by X nondisjunction and reduces recombination 
on the X-chromosome specifically. Worms carrying h134 in trans to e879 
are very sick and produce 10 - 20% males. e879 is slightly 
semidominant with e879/+ giving 1 - 2% male progeny. Our lethal 
alleles also behave semidominantly: h134/+ produces about 1% males and 
+(sDp2)/h134/h134 produces 1 - 2 % males. Interestingly, sDf4, which 
deletes him-l, also has a mild Him phenotype. It is surprising that a 
gene which was thought to affect only the X-chromosome would have 
lethal alleles. One hypothesis is that the wild type him-l gene 
product is required for proper pairing, recombination and segregation 
of all chromosomes at meiosis. e879 may be a weak hypomorphic allele 
which can take care of the autosomes but can't manage the X. Our 
lethals could be loss of function alleles which do not allow meiosis 
to proceed at all, leading to sterility. We will use sup-7 [Waterston (
1981) Genetics 97: 307-325] to try to determine if these are amber 
To update the last newsletter note about gamma-induced sDp2 lethals -
- None of the lethals fails to complement more than one 
complementation group. If any of them are deficiencies, they must be 
small. It may be that sDp2 is not very good at rescuing deficiencies. 
We are currently analyzing a set of gamma-induced lethals balanced 
over szT1 (I;X).