Homothallismus in fungi is the ability to mating type change. In contrast, the Heterothallie.

The example of the yeast Saccharomyces cerevisiae: haploid cells can be either the mating type a or α own. During the mating of two haploid cells are necessary partners of different mating type. However, a homothallic mother cell has the ability to switch their mating type ( mating- type switching) and then to mate with their incurred by budding daughter cell.