No, yeast is not exclusively diploid. According to the provided reference, yeast cells can stably exist in either a diploid or a haploid form.
In other words, yeast can exist in two forms, one with a single set of chromosomes (haploid) and one with two sets of chromosomes (diploid). This ability is related to yeast mating types and life cycle.
Here's a breakdown:
- Haploid Yeast: Haploid yeast cells have only one set of chromosomes. They possess a mating type, either a or α (alpha). These cells can undergo mitotic division (asexual reproduction).
- Diploid Yeast: Diploid yeast cells have two sets of chromosomes. They are formed when haploid a and α cells fuse together (sexual reproduction). Diploid yeast cells can also undergo mitotic division. Diploid cells can undergo meiosis (reduction division), resulting in haploid cells.
| Characteristic | Haploid Yeast | Diploid Yeast |
|---|---|---|
| Chromosome Number | One set (n) | Two sets (2n) |
| Mating Type | a or α | None (formed by a and α fusion) |
| Reproduction | Asexual (mitosis) | Asexual (mitosis) |
| Formation | Arises from meiosis of a diploid cell or mitotic division of an existing haploid cell. | Formed by fusion of a and α haploid cells. |
