Ascomycete Yeast Life Cycle

Ascomycete Yeast also called as saccharomyces cerevisiae have been studied clearly defined and experimentally manipulable fungi life cycle. Life cycle of this yeast involves mitotically propagating haploid forms of two distinct mating types, and a diploid form that can either grow vegetatively or be induced into a meiotic developmental pathway through manipulation of the nutrient conditions of the growth medium. The cellular pathways processes such as mitotic proliferation, cell recognition and mating, meiosis and sporulation have been extensively studied on a molecular level.

The growth of the yeast cell involves build a budding. During this process growth of the cell is directed to a specific location on the surface of the mother cell, and a new cell is formed somewhat like blowing up a balloon through a hole in the mother cell. Highly polarized growth of the developing daughter cell, implicating both the acting and microtubule based cytoskeletal networks, and is tightly coordinated with the cell cycle. Both haploid and diploid cells divide by the budding process, although there are subtle differences in the choice of the sites of bud emergence between haploids and diploids. In addition, some diploid cells can also modify the coordination of the cell cycle and polarized growth to switch to a pseudohyphal growth mode. In this growth pattern individual cells are more elongated, and the budding pattern leads to the formation of chains of cells rather than compact colonies characteristic of the true budding mode.

On the vegetative growing haploid cells of opposite mating types are brought into proximity, they communicate to each other by diffusible pheronomes, synchronize their cell cycles, conjugate and then fuse their nuclei to create non mating, meiosis proficient diploids. These diploids can be identified visually in their initial zygotes form, and separated from the haploids by micromanipulation, or identified selectively because they contain a pattern of genetic traits not possessed by either haploid parent.