Fig. 2.

Routes of mating-type chromosome evolution in Microbotryum. Model for mating-type chromosomal rearrangement events, as inferred from comparisons with the two mating-type chromosomes of M. lagerheimii (used as a proxy for the ancestral mating-type chromosomes in the genus¹⁶). Mating-type chromosome content across Microbotryum species is illustrated by colors referring to different parts of the two M. lagerheimii mating-type chromosomes (Supplementary Figs. 5–8). The inferred ancestral locations of putative centromeres and mating-type loci are indicated in yellow and black, respectively, and the regions of suppressed recombination are dashed. Chromosome sizes are indicated by their relative scales; the last stage in the evolution of recombination suppression often involves increases in chromosome size due to the accumulation of repetitive elements. Mating-type chromosome evolution in a M. lychnidis-dioicae, b M. silenes-acaulis, c M. violaceum caroliniana, d M. scabiosae, and e M. v. paradoxa, in which the top edge of the mating-type chromosome corresponds to a rearrangement from the middle of the chromosome, supporting complete recombination suppression up to the end of the chromosome