Worm Breeder's Gazette 7(1): 80

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Studies with dpy-21

P. Meneely

Figure 1

Animals homozygous for dpy-21 V are Dpy if they have two X 
chromosomes (X:A = 1.0), but nonDpy if they have only one X (X:A = 0.5)
, irrespective of sexual phenotype.  Somehow the autosomal dpy-21 
locus appears to respond to the ratio of X chromosomes to sets of 
autosomes (X:A ratio; Hodgkin, Genetics 96:649-664, 980).
I have used the X-linked duplications from Minnesota in attempts to 
determine whether a specific region, or simply the total amount of X 
chromosomal material is being counted.  The basic idea is to construct 
mnDP(unc+)/+; him-5 unc X stocks and to look at 
the nonUnc male progeny which will have one X plus the duplication.  
If the duplication is not counted as an X chromosome (either because 
it is too small or because it lacks the crucial regions, these males 
will be nonDpy; this result is found for mnDp1, 
is counted as an X chromosomes, these males will be Dpy.  Both mnDp10 
and mnDp25 may fall into this class, because each gives a few Dpy 
males, and some semiDpy males.  As seen in the map and the table, both 
mnDp10 and mnDp25 include a region to the left of unc-9; however, they 
are also apparently the largest duplications, based on the map 
distance between duplicated markers, a crude estimate at best.  Thus, 
dpy-21 responds to these two duplications at least partly as X 
chromosomes, either because they carry a region to the left of unc-9 
or because they represent a substantial amount of X material.
An experiment designed to discriminate between these possibilities 
has given only preliminary results so far.  I have attempted to 
construct a stock that has both mnDp33 and mnDp9; neither of these by 
itself is counted as an X, but together they represent about as much X 
material as mnDp10.  The last step in the construction was to mate 
mnDp33/+; him-5 unc-20/0 males to mnDp9/+; him-5 
unc-20, odites.  The 
males from this cross will include some nonUnc-20 nonUnc-3 males that 
have both duplications; all other males will be Unc-3 or Unc-20 or Unc-
20 losely resembles Unc-3).  There were 6 
nonUnc males and all were Dpy, suggesting that mnDp33 and mnDp9 
together are counted as an X chromosome.  Unfortunately, these males 
did not mate, so I could not make an hermaphrodite stock with both 
A straightforward interpretation of these results would be that in 
responding to the X:A ratio, dpy-21 does not distinguish between one X 
plus 25%-30% of an X (X:A=0.65% and 2X (X:A=l).  However, this view 
appears contrary to Jonathan Hodgkin's observation that 4A:4X 
tetraploid dpy-21 hermaphrodites (X:A=l) are Dpy, while 4A:3X dpy-21 
hermaphrodites (X:A=0.75) are nonDpy (ibid.).  The two sets of 
observations can be reconciled by somewhat fancier models, for example,
by assuming that the crucial X material is not homogeneously 
distributed along the X.
[See Figure 1]

Figure 1