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Ascomycota Reproduction: Ascus & Ascospore

Instructor: Lauren Posey

Lauren has taught intermediate reading in an English Language Institute, and she has her Master's degree in Linguistics.

Have you ever thought about how yeast reproduces? That's what you'll learn in this lesson! We will look at the reproduction of Ascomycota, a group of fungi that includes yeast.

A Variety of Fungi

What do yeast, penicillin, and Dutch Elm disease have in common? They are all fungi! Specifically, these fungi are all members of the phylum Ascomycota. Ascomycota is a huge group, including more than 32,000 different species of fungus. In addition to yeast and penicillin, it also includes edible fungi such as morel mushrooms and truffles, as well as less appetizing fungi such as bread molds (penicillin is actually made from a type of mold that can grow on bread). Despite the wide range of species within this group, all the members share a few common characteristics, particularly their methods of reproduction.

Morel mushrooms are a member of the Ascomycota group.
Morel mushroom

Ascomycota Reproduction

Ascomycota have two methods of reproduction: asexual and sexual. Most Ascomycota can reproduce using either method or even using both. In asexual reproduction, the fungus undergoes budding or fission, where cells from the fungus divide and split, forming new, genetically identical fungi that can then break off and grow on their own. The spores, or fungal seeds, formed by asexual reproduction are called conidia, and this process allows the fungus to reproduce more quickly than sexual reproduction alone.

All Ascomycota fungi can reproduce sexually. In fact, the ascus, a sac-shaped cell formed as part of the sexual reproduction process, is what gives this group its name. In sexual reproduction, two different gametes, or sex cells, have to combine for reproduction to begin. In some species, the second gamete has to come from another fungus. In other species, a single fungus contains both male and female gametes and can self-fertilize.

The Ascus

The microscopic ascus forms as part of sexual reproduction after the two gametes have combined. The zygote (the single cell created when the gametes combine) develops inside the ascus and divides two to three times, eventually creating either four or eight new cells, each of which is an individual spore.

A single fungus can have many separate asci. In a number of Ascomycota species, the asci all grow in the same place, within a cup or bulge on the surface of the fungus, which is called the ascocarp. Unlike asci, an ascocarp can be seen without having to use a microscope. An ascocarp can look like an open cup, it can be a completely closed bulge on the fungal surface, or it can be only partially open. The shape of the ascocarp depends on the species of fungus.

Ascospores

The spores formed inside the ascus as a product of sexual reproduction are called ascospores. There are typically only eight ascospores in each ascus, but since there can be many asci, each fungus might have hundreds of ascospores.

There are usually eight ascospores per ascus.
Ascospores

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