Worm Breeder's Gazette 7(2): 24

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Two Notes on Sex Determination

J. Hodgkin

Figure 1

l) An almost invisible tra-2 
In the course of mapping a dominant mutation, dpy-25(e8) I found 
that the original isolate CB817 carried a weak tra-2 allele, e1875, 
which was easily separated from e817.  The phenotype of heterozygotes 
with strong tra-2 alleles, e.g.  e1875/e1425 is similar to that of tra-
2 (f70) ( = tri of Beguet and Gibert, 1978), i.e.  a self-fertile 
hermaphrodite with a variably masculinized tail.  However, the 
homozygote e1875/e1875 is anatomically indistinguishable from a wild-
type hermaphrodite, thus it is a 'subliminal' allele.  The interesting 
difference from wild type is that the self-progeny broods of e1875 
hermaphrodites are more variable in size and on average larger than 
wild type (N2)
[See Figure 1]
This may indicate that one of the wild type functions of tra-2 is to 
control the number of sperm made by the hermaphrodite.  The larger 
brood size does not mean that e1875 is a 'better' strain than N2 and 
in fact N2 grows faster, as judged by its consistent victories in 
eating races between the two strains.
2) Male chauvinist 
Two mutants abducted from MIT, n198 and n199, prove to be alleles of 
a new dumpy gene, dpy-26 IV.  These mutants have strange properties: 
homozygotes derived from a heterozygous dpy-26/+ parent are fully 
viable and only slightly dumpy, but their self progeny consist of many 
dead eggs and larvae, a few severely dumpy hermaphrodites which are 
usually infertile, and a few (0 to 15) non-dumpy males.  Homozygous 
stocks are almost impossible to maintain.  As with dpy-21 V,it is the 
number of X chromosomes that determines the phenotype: tra; dpy-26 XX 
males are dumpy, and her; dpy-26 XO hermaphrodites are non-dumpy.  
Therefore, dpy-26 appears to be a maternal effect XX lethal.  However, 
the mutation has some effect on XO animals: both dpy-26 XO males and 
dpy-26; phrodites are less fertile than the 
equivalent wild-type or dpy-21 strains.
The similarities between dpy 26 and the Drosophila mutant 
daughterless (see Genetics 96: 903-926 and other T.  Cline papers) are 
distinctly intriguing.
There are also similarities between dpy-26, 
animals, both in dumpy phenotype and in 
partially suppressing Tra phenotypes.  The dpy-21 XXX combination 
appears to be lethal, but dpy-26,dpy-21 XX is viable (for the first 
It is curious that dpy-26 should have a Him phenotype (both alleles 
and the heterozygote n198/n199).  One possibility that can be excluded 
is that the Him-ness is a consequence of pre-meiotic selection for XO 
germ cells: if this were the case, then a dpy-26, 
aphrodite should tend to give jackpots of all 
wild or all Unc males, and this was not observed.

Figure 1