The Caenorhabditis elegans mutation
e873, which results in a recessive uncoordinated phenotype (formerly named Unc-72) and which had been isolated after 32P treatment (Brenner 1974), has now been found to act as a crossover suppressor and to be associated with a translocation between linkage groups (LG's) III and V. The translocation has been named, eT1(III; V); eT1 acts as a dominant crossover suppressor for both the right half of LGIII and the left half of LGV, providing a balancer for a total of 39 map units. The uncoordinated
e873 phenotype has been shown to be a consequence of an inactive unc-36III gene. It was possible to demonstrate that, in translocation heterozygotes, eT1 chromosomes marked with either
sma-3 or
dpy-11 segregate from normal LGIII, while those marked with
bli-5,
sma-2 or
unc-42 segregate from normal LGV. Since
bli-5 and
sma-2 are normally on LGIII, and
dpy-11 is normally on LGV, it is concluded that: (a) eT1 is a reciprocal translocation; (b) there is a breakpoint between
sma-3 and
sma-2 in LGIII (the region containing
unc-36) and one between
dpy-11 and
unc-42 in LGV; (c) there is no dominant centromere between
sma-2 and
bli-5 on LGIII, since in eT1 these genes are not linked to a LGIII centromere. Similarly, it is highly unlikely that there is a centromere to the left of
dpy-11 on LGV. The new gene order in eT1 was determined by measuring recombination rates between markers in eT1 homozygotes. It is concluded that the new order is:
dpy-1 sma-3 (break)
dpy-11 unc-60, and
bli-5 sma-2 (break)
unc-42 unc-51.--This is the first analysis of a C. elegans translocation with respect to reciprocity, breakpoints and new gene order.