We have isolated a transgenic that produces a high proportion of self-progeny males due to a defect in segregation of the X chromosome. The gene responsible for this phenotype is encoded by C05D2.5, which is located to the right of
dpy-17 on chromosome III (Left). RNAi assays confirm the role for this gene in meiotic chromosome segregation as worms treated with C05D2.5 dsRNA also exhibit a high proportion of self-progeny males. Chromosome defects are not seen in prophase I of meiosis and therefore, this gene must be acting at some point past this phase. Furthermore, recombination, which occurs during prophase I, proceeds normally. C05D2.5 expression is enhanced in the germline. Furthermore, chromosome segregation abnormalities occur only in the oocyte line of the hermaphrodite and involve the autosomes as well as the X chromosome. Our numbers indicate that there is a high incidence of chromosome loss, however, it appears that chromosomes do segregate in a normal fashion most of the time. We are currently testing whether the phenotype produced by this transgenic is a result of co-suppression. We are also attempting to look at the one-cell embryo to observe any chromosome or spindle defects in meiosis I or II that occur after fertilization in these transgenic animals.