ABSTRACT
The T(EB4)Nta, T(IBj5)Nta, and T(B362i)NtA strains were constructed by introgressing the insertionaltranslocations EB4, IBj5, and B362i from Neurospora crassa into the related species N. tetrasperma. Theprogeny from crosses of T(IBj5)Nta and T(B362i)NtA with opposite mating-type derivatives of the standard N.tetrasperma strain 85 exhibited a unique and unprecedented transmission ratio distortion (TRD) that disfavoredhomokaryons produced following alternate segregation relative to those produced following adjacent-1 segregation. The TRD was not evident among the [mat A ? mat a] dikaryons produced following either segregation. Further, crosses of the T(IBj5)Nta and T(B362i)NtA strains with the Eight spore (E) mutant showed anunusual ascus phenotype called ‘max-4’. We propose that the TRD and the max-4 phenotype are manifestations of the same Bateson-Dobzhansky-Muller incompatibility (BDMI). Since the TRD selects against 2/3 ofthe homokaryotic progeny from each introgression cross, the BDMI would have enriched for the dikaryoticprogeny in the viable ascospores, and thus, paradoxically, facilitated the introgressions.