How Does Yeast Reproduce

Yeast is a type of unicellular fungi mostly used in the baking and brewing industry due to its ability to ferment sugars into ethanol and carbon dioxide. Yeats undergo both asexual and sexual reproduction. Asexual reproduction method of yeast is well known and is called budding. Sexual reproduction of yeast is called mating. Haploid yeast cells with different genders fuse together to form a diploid cell. Diploid yeasts produce haploid yeasts during unfavorable conditions.

Key Areas Covered

1. What is Yeast
     – Definition, Characteristics
2. How Does Yeats Reproduce
     – Asexual Reproduction, Sexual Reproduction

Key Terms: Budding, Diploid, Haploid, Mating, Shmooing, Spores, Yeast

What is Yeast

Yeast is a microscopic fungus comprising a single oval-shaped cell. Generally, yeast is colorless. They belong to the kingdom of Fungi. Hence, yeast is a eukaryote that contains membrane-bound organelles. Yeast can be naturally found in a variety of habitats, especially on plant leaves, flowers, and fruits. Some yeast live in symbiotic relationships on the skin of warm-blooded animals. A few of them may live as parasites. For example, Candida albicans causes vaginal yeast infections. 

How Does Yeast Reproduce

Yeasts undergo both asexual reproduction and sexual reproduction. There are two types of cells in a yeast population: haploid cells and diploid cells. Haploid yeast cells consist of a single set of homologous chromosomes within the nucleus. However, diploid yeast cells consist of two sets of homologous chromosomes. Haploid yeast cells exist in two genders.

Asexual Reproduction of Yeast

Asexual reproduction of yeast mainly occurs by budding or fission. Standard cell division occurs during budding. The parent nucleus divides into two daughter nuclei by mitosis. Thus, the number of chromosomes in daughter nuclei is similar to that of the parent nucleus. During budding, the daughter cell first appears as a small outgrowth since one daughter nucleus migrates to a corner of the parent cell. Since a bud-like structure appears from the parent cell, this type of budding is called asymmetric budding. Both haploid and diploid cells can undergo budding. Haploid parent cells give rise to haploid daughter cells while diploid parent cells give rise to diploid daughter cells.

Figure 1: Yeast Budding

Sexual Reproduction of Yeast

Only haploid cells undergo sexual reproduction. Haploid cells undergo a process called shmooing in which they become longer and thinner while preparing to join. Haploid cells with different gender fuse together to form a diploid yeast cell. The fusion of haploid yeast cells is called sexual conjugation or mating. The diploid cell then undergoes mitosis to form a colony of diploid yeast cells.

Figure 2: Yeast Reproduction
Budding, 2. Mating, 3. Spore Production

When there is a danger of desiccation, diploid yeasts produce spores. The diploid nucleus undergoes meiosis to form four haploid daughter nuclei. Generally, the protoplasm of the parent yeast cell divides into four portions surrounding the four daughter nuclei. Each portion is then surrounded by a thick cell wall. Since the division of the protoplasm produces these spores, the resultant spores are called endospores. They can tolerate unfavorable conditions. Upon germination, spores give rise to a chain of cells, which are haploid. Haploid cells are unable to tolerate unfavorable conditions.

Conclusion

Yeats is a type of unicellular fungi widely used in the baking and brewing industry. They undergo ethanol fermentation. Both haploid and diploid cells can be identified in a yeast population. Yeast reproduces by two main methods. Both types of yeast cells undergo asexual reproduction by budding. Haploid yeast cells with different genders fuse together to form a diploid cell. This diploid cell undergoes mitosis to produce a population of diploid yeast cells. During unfavorable conditions, diploid yeast cells produce haploid endospores. Upon germination, they give rise to haploid yeast populations.

Reference:

1. “Reproduction in Yeast (With Diagram) | Fungi.” Biology Discussion, 17 Oct. 2016, Available here.

Image Courtesy:

1. “S cerevisiae under DIC microscopy” By Masur – Own work (Public Domain) via Commons Wikimedia
2. “Yeast lifecycle” By pl.wiki: Masurcommons: Masurirc: [1] – Own work (Public Domain) via Commons Wikimedia

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