spontaneous diploidization

[LEIBOWITZ at OCELOT.RUTGERS.EDU]

Although as noted, the ho strains used in most yeast labs only rarely
spontaneously switch mating type, I have had this happen to me at least once,
and sporulated the resulting diploid to make handy isogenic a and alpha
testers, which have been stable for 20 years (indicating the relative rarity of
such events).

Mike Leibowitz
RW Johnson Medical School