A novel meiotic drive in Neurospora crosses heterozygous for hybrid translocation strains disfavors homokaryotic progeny derived from alternate, but not adjacent-1 segregation.

Four insertional or quasiterminal translocations (T) were recently introgressed from Neurospora crassa into N. tetrasperma. Crosses of two of the resulting TNt strains with N. tetrasperma N strains (N = normal sequence) produced more Dp than T and N homokaryotic progeny, although [T + N] and [Dp + Df] heterokaryotic progeny were made in roughly equal numbers. The T, N, and [T + N] progeny are derived from alternate segregation (ALT), whereas adjacent-1 segregation (ADJ) generates the Dp, Df, and [Dp + Df] types. Differential recovery of homokaryotic products from ALT and ADJ represents a novel and unprecedented type of meiotic drive. This drive contributed to our inability to introgress a larger insertions translocation, T(VR>VIL)UK3-41, into N. tetrasperma. We suggest that one or more Bateson-Dobzhansky-Muller type incompatibility between N. crassa and N. tetrasperma genes in the TNt x N crosses might cause an insufficiency for a product required for ascospore maturation. Since the Df type is inviable, only four ascospores (Dp or [Dp + Df] types) share this limited resource in [Dp + Df] asci, whereas four to eight ascospores compete for it in [T + N] asci. This increases the chance that in asci with >4 ascospores none properly matures, and results in Dp progeny out-numbering T and N types.