A combination inversion and translocation in Neurospora crassa with inviable deficiency progeny that can be rescued in heterokaryons.

Chromosome rearrangement In(IL;IR)T(IL;IIIR)SLm-1, has a pericentric inversion in linkage group I associated with a reciprocal translocation between I and III. The rearrangement was identified cytologically in pairing with normal sequence chromosomes at pachynema. Rearrangement breakpoints were mapped genetically in IL, IR and IIIR by crosses with normal sequence strains and in crosses with an inversion that partially overlaps the SLm-1 inversion. When rearrangement SLm-1 is crossed to parents with normal sequence chromosomes, one class among the progeny has a small chromosome deficiency and large duplication. The ascospores containing this deficiency/duplication die either before germination or just after, when growth commences. Germ tubes of the deficiency/duplication progeny, which start to grow then stop, resemble the aborted growth of auxotrophic mutants germinated on minimal medium. Efforts to correct the deficiency with nutritional supplements were not successful. However, the defective class can be rescued by fusing the germinating hyphae of the deficiency ascospore with a complementary auxotrophic mutant to form a heterokaryon. A deficiency/duplication nucleus that is rescued in a heterokaryon can serve as a fertilizing nucleus in crosses with a normal sequence parent. One half of their progeny have the normal chromosome sequence and one half have the chromosome deficiency syndrome and die at germination.