The latter is comprised of two unlinked mating type loci, locus A (which also has HD1 and HD2 genes) and locus B, which usually contains pheromone receptor gene and pheromone pre-cursor gene (Kües et al., 2011). Mating compatibility, leading to heterokaryosis and fruiting, exists only between mycelia carrying different mating type genes and is the basis of cross-breeding