Mitotically unstable polyploids in the yeast Pichia guilliermondii

Attempts to obtain triploids or tetraploids of P. guilliermondii by sexual hybridization led to mitotically stable hybrids. However, their DNA content per cell was not higher than in diploids. The results of random spore analysis demonstrate that these hybrids were in fact aneuploids which obviously suffered drastic chromosome losses immediately after mating. This phenomenon could have been caused either by aneuploidy already present in the parental strains or it might have been due to a general inability of P. guilliermondii to maintain a polyploid genome.