XVI International Botanical Congess

N. tetrasperma ascospores are heterokaryotic for mating type and produce self fertile progeny (Dev Genet 15:104). Prior studies in our laboratories showed a major part of the mating type chromosome does not crossover, but a single obligatory crossover occurs on the far left arm. Introgression of A and a mating type chromosomes from N. crassa into N. tetrasperma results in loss of the recombination block showing N. tetrasperma autosomes alone are not responsible for blocked recombination. Reciprocal experiments show recombination on N. tetrasperma mating type chromosomes in a N. crassa autosomal background ruling out a causal dominant genetic factor on this N. tetrasperma chromosome. Introgressions are being tested for recessive factors on the N. tetrasperma mating type chromosome and interactions between autosomes and the mating type chromosome.