Worm Breeder's Gazette 6(1): 21
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In the last issue we reported about a chromosome rearrangement (then called Bal-X-I; the new name is szT1), which : 1. suppresses crossover in the dpy-8 f the X chromosome; 2. is marked with lon-2 (e678); 3. is homozygous lethal; 4. as hemizygous (her-1) hermaphrodite is sterile; 5. as hemizygous male is viable and fertile; 6. segregates about 8-20% of males. We are interested to know whether szT1 is an inversion, translocation or free duplication. If it were a homozygous lethal inversion, 25% egg lethality could be expected. If it were a free duplication, the population would tend to lose the balancer chromosome. However, if it were a translocation, a high rate of embryo mortality could be expected. In an experiment eggs were collected from young szT1 immediately and viable adult progeny were scored two days later. From 1233 fertilized eggs counted, 385 viable adult progeny developed (31%). This finding suggests that szT1 might be a translocation. In pseudolinkage experiments we wanted to establish which autosome is involved in this translocation. Double mutants homozygous for unc-3 ( e151) and different dpy alleles from different linkage groups were combined and crossed out with szT1 (lon-2) males. The frequencies of recombination between lon-2 and the autosomal dpy alleles were studied. (Only the males were scored, because all male categories were viable. ) [See Figure 1] This corresponds to p = 0.5 between unc-3 and the autosomal markers, and p = 0.5 between lon-2 and markers of LG II, III, IV and V, but p between lon-2 and dpy-5 (I.) was 0. We concluded that the szT1 chromosome is an (X;I) translocation.