Saccharomyces cerevisiae is a diploid yeast species, which means that it has two copies of each chromosome. To form gametes, S. cerevisiae cells must go through a process called meiosis.
Meiosis is a type of cell division that results in the formation of four genetically diverse haploid cells, each with half the number of chromosomes as the parent cell.
The steps the cells will follow to form gametes are:
Prophase I: The chromosomes condense and become visible under a microscope. Homologous chromosomes pair up and exchange genetic material through a process called crossing over.
Metaphase I: The homologous chromosomes line up at the center of the cell.
Anaphase I: The paired homologous chromosomes are separated and pulled to opposite poles of the cell.
Telophase I: The chromosomes reach the poles and the cell begins to divide.
Cytokinesis: The cell physically divides in two, forming two haploid cells.
A second round of cell division, called meiosis II, takes place in which the chromosomes are again separated resulting in the formation of four haploid cells.
It's worth to mention that, yeast cells are capable of switching between sexual and asexual reproduction depending on environmental conditions. The formation of meiotic spores depends on the presence of specific nutrients, mating partners and stress.