Evolutionary erosion of yeast sex chromosomes by mating-type switching accidents

摘要: We investigate yeast sex chromosome evolution by comparing genome sequences from 16 species in the family Saccharomycetaceae, including data genera Tetrapisispora, Kazachstania, Naumovozyma, and Torulaspora. show that although most contain a mating-type (MAT) locus silent HML HMR loci structurally analogous to those of Saccharomyces cerevisiae, their detailed organization is highly variable indicates MAT deletion hotspot. Over evolutionary time, chromosomal genes located immediately beside have continually been deleted, truncated, or transposed other places process gradually shortening distance between HML. Each time gene removed transposition, next on brought into proximity with turn put at risk for removal. This has also replaced triplicated sequence regions, called Z X, allow be used as templates DNA repair during switching. propose transposition events are caused accidents switching, combined natural selection keep same chromosome. The rate accelerated greatly after whole-genome duplication, probably because were redundant could deleted without requiring transposition. suggest that, despite its mutational cost, switching confers an benefit providing way isolated germinating spore reform spores if environment too poor.