Fig. 1

Preparation of materials for estimation of mutation rates in Neurospora crassa. a Experimental design. The asexual cycle includes the germination of vegetative spores (conidia), formation of mycelia, emergence of conidiophores, and further formation of conidia. The sexual cycle involves two spores (either asexual conidia or sexual ascospores) of opposite mating types, mating type A (blue) and mating type a (red). When subject to nitrogen starvation, either mating type can form “female” structures for the opposite mating type to fertilize and initiate development of perithecia. The nuclei of two mating types would coexist in the same cytoplasm and undergo mitoses before fusion. A meiotic division followed by a mitotic division would be initiated immediately after the fusion of two haploid nuclei, which generates the ascus with eight ascospores. Illustration based on Aramayo and Selker [15]. Dashed arrows: some intermediate steps are not shown. The approximate stages covered in each experiment are indicated below. For crossing lines, four non-mitotic sister spores (1~4) were sequenced. For cross group G, the two parents were selected from the products of cross group C (e.g., ascospore 1 and 4). b SNP phylogeny of parental strains used to generate the six crosses. Two parental strains for each cross are connected by dashed lines, with the estimated diversity given in proximity. The cross ID and numbers of sequenced asci (× 4 non-sister spores) are given in parentheses. The phylogenetic tree was constructed using SNP sites only (neighbor-joining method, 1000 bootstrap replicates)