FIGURE 1: Life cycles of budding yeast (Saccharomyces cerevisiae) (A) and fission yeast (Schizosaccharomyces pombe) (B). Diagrams show yeasts have both asexual (vegetative) and sexual reproductive cycles, respectively. (A) Budding yeast is generally maintained in the laboratory through vegetative growth both as haplontic (haploid) and diplontic (diploid) cells during asexual life cycle by mitosis, which produce daughter cells by budding off of mother cells. Mitotic cell cycle has all of the typical eukaryotic cell cycle stages of G1, S, G2 and M phases, but it spends most of its cell cycling in G1 phase, which is similar to human cell cycle. Under stressful conditions, diploid cells undergo meiosis to form haploid spores by sporulation. Haploid cells of opposite mating types (a or α) can go on to mate (conjugate) and to reform diploid cells. (B) Fission yeast is normally present as haploid cells through mitosis. Cells are divided equally between daughter and mother cells. In contrast to budding yeast cell cycle, fission yeast spends most of its cell cycling in G2 phase. Its diploid form could be triggered by stress through mating of opposite mating type (h⁺ or h^–) during meiosis.