Extensive Trans-Specific Polymorphism at the Mating Type Locus of the Root Decay Fungus Heterobasidion

“…Some basidiomycete species have incorporated the genes that encode the pheromone and pheromone receptor proteins into the mating-type locus (Raudaskoski and Kothe, 2010). With the exceptions discussed below, crossing-over is not known to occur within the mating-type loci, where the intercompatibility of alternate alleles maintains the divergent forms and even ancient trans-specific polymorphisms (Devier et al , 2009; van Diepen et al , 2013), to the extent that homology is sometimes difficult to recognize or has been questioned (Metzenberg and Glass, 1990; Debuchy et al , 2010). This feature resembles the mammalian sex chromosomes, yet in fungi the mating compatibility of the cell type can be defined by as little as 1 kb of DNA rather than the majority of the chromosome (Butler, 2007).…”