Fungal genome and mating system transitions facilitated by chromosomal translocations involving intercentromeric recombination
(I) In the ancestor, the P/R and HD loci were located on different chromosomes, which had regional centromeres that shared common transposable/repetitive elements. (II) and (III) Ectopic recombination occurred between the 2 chromosomes within the centromeric regions, possibly mediated by the common transposable/repetitive elements, bringing the 2 mating type (MAT) loci onto the same chromosome. (IV) Subsequent chromosomal rearrangements (e.g., inversions and transpositions) bring the 2 MAT loci next to each other. (V) Eventually the P/R and HD loci fuse to form a single contiguous MAT locus that is present in the derived bipolar mating system. (VI) The resulting chromosome with the contiguous MAT locus could undergo additional intercentromeric recombination events. The numbers in the parentheses next to the “CEN” indicate the C. amylolentus chromosome on which those centromeric flanking regions are located.