Figure 1. Diversity and phylogeny of MAT gene alleles in S. salmonicolor.

(A) Phylogeny of HD1/HD2 genes. Mating types A1, A2, and asexual strains are designated as A1, A2 and AS, respectively. Boxes designate the various HD1/HD2 alleles with numerals after the mating type designation. Circles after strain numbers depict the type of pheromone receptor gene (yellow, STE3.A1; blue, STE3.A2). Asterisks indicate the two instances where common ancestry of HD1/HD2 alleles associated with opposite mating types is best supported. (B) Comparison of the number and distribution of MAT gene alleles in emblematic species representing the different mating systems (HD, homeodomain region; PR, pheromone receptor region; the continuous or discontinuous line between the HD and PR boxes denotes genetic linkage or its absence, respectively).