In fungal development, the mushroom-forming basidiomycetes show fruiting body development depending on the mating of two compatible mates. The tetrapolar mating system depends on two independent loci, A and B, which consist of multiple subloci with numerous specificities that independently, but redundantly, determine mating type. The interactions between homeodomain transcription factors in A and the pheromone recognition of several G-protein-coupled receptors (GPCRs) in B are the molecular basis of sexual development, respectively. Especially with the well-characterized model systems Coprinopsis cinerea and Schizophyllum commune, additional pheromone-receptor-like genes encoded in the vicinity of the B locus have been found. The involvement of those genes—which, in contrast to the mating type genes, do not differ between strains of different specificity—was shown with respect to self-recognition and self-avoidance in mycelial growth, and in the development of true clamp connections that are involved in maintaining a dikaryotic life style of mated mycelia, albeit not all basidiomycete show clamped dikaryotic mycelia at all times. Hence, the specifics of mating, the new nonmating receptors, and clamp formation are specifically discussed here.