The Nakaseomyces clade includes Candida glabrata, a major fungal pathogen of immuno-compromised patients, and five other species, two of which have recently also been identified as human opportunistic pathogens. The genome of C. glabrata was published in 2004, and we have recently sequenced the genomes of all other known species of the Nakaseomyces genus. This clade is much closer to Saccharomyces cerevisiae than to the major Candida clade that includes C. albicans. Indeed, the Nakaseomyces derive from the same ancestor as S. cerevisiae that underwent a whole-genome duplication event, and their genomes contain the elements needed for mating-type switching in S. cerevisiae. These consist of mating-type cassettes of both types in haploid genomes, and the HO gene, that encodes the endonuclease initiating the switching event. Nonetheless, the four “Candida” species within the clade have been described as asexual, and no mating-type switching has been directly observed in any species. All Nakaseomyces seem to be haploid, except one. All indeed contain copies of opposite mating-type loci in haploid genomes, but there are structural differences between species. We have induced switching in C. glabrata by heterologous expression of various HO genes, and observe high lethality of cells, and mating-type switching “accidents”, that result in aberrant structures of cassettes, in survivors.