A transmission ratio distortion and the 'max-4' ascus phenotype: Do both reflect the same Bateson-Dobzhansky-Muller Incompatibility emerging during trans-species introgression of translocations in ?

The T(EB4)a, T(IBj5)a, and T(B362i)NtA strains were constructed by introgressing the insertional translocations EB4, IBj5, and B362i from Neurospora crassa into the related species . The progeny from crosses of T(IBj5)a and T(B362i)A with opposite mating-type derivatives of the standard N. tetrasperma strain 85 exhibited a unique and unprecedented transmission ratio distortion (TRD) that disfavored homokaryons 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)a and T(B362i)A strains with the Eight spore (E) mutant showed an unusual 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 of the homokaryotic progeny from each introgression cross, the BDMI would have enriched for the dikaryotic progeny in the viable ascospores, and thus, paradoxically, facilitated the introgressions.