Figure 1. Genetic Map of the N. tetrasperma Mating-Type Chromosome Showing Markers used in this Study.

A. Left arm of the chromosome is positioned towards the top. Gene order as assumed from the N. tetrasperma mat a- chromosome of single mating-type component P581a (2509). Markers with asterisks (*) were also used in the genealogy study; mep (boxed) was only used as a phenotype marker in crosses. The two d _S-defined evolutionary strata of strain P581 along the chromosome are indicated and numbered. Numbers to the left of markers ro-10–mat indicate crossover-frequencies when the mat a-chromosome of the mat a-component strain of P581 was introgressed into N. crassa background and crossed with a N. crassa mat A strain. B. One most parsimonious tree of each of the five selected genes of the old stratum. The 12 strains used are single mating-type components of six wild-type N. tetrasperma heterokaryons belonging to two different phylogenetic lineages [20]. For clarity, each strain is referred to by the original heterokaryon number followed by the appropriate mating type (mat A or mat a; Table 1). Bars indicate number of changes, and numbers by branches indicate bootstrap values of above 50% (1000 replicates).