03/05/2021
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Transcript: Fungi Propagation: Sexual & Asexual Life Cycles
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Not every organism gets to decide between reproducing sexually or asexually, and that makes fungi pretty special. In
this lesson we are going to look at different forms of fungi propagation and discover how each works, as well as when
and why fungi use each.
Fungi Propagation
Where do baby fungi come from? Well, when a mommy fungus and a daddy fungus love each other
very much…or when just one fungus is lonely…well there's this stork, see? Hmm. This is going to be
harder than I thought. As it turns out, fungi, nonphotosynthetic organisms that decompose food before
absorbing it, have a lot of choices when it comes to reproduction. This is because most fungi can
reproduce both sexually, requiring two parents to mix genes, and asexually, with only one parent. Not
many living things can do both, but the fungi can.
Either way, most fungi reproduce using spores, tiny reproductive units capable of growing into mature
organisms. Spores are sort of like seeds, but smaller and lighter. Some fungi can release literally trillions
of spores at a time, which are dispersed over wind or water or by latching onto passing creatures. I
guess that means that a stork actually could deliver a baby fungus.
Asexual Reproduction
Fungi are unique in being able to reproduce both sexually and asexually. So, how do each of these
systems work? Well, let's start with asexual reproduction, which is sort of the default setting for fungi.
When conditions are favorable, so when the environment is moist and there are plenty of nutrients for
the fungus to feed on, then it will reproduce asexually. It does this by creating haploid spores, meaning
they only have one set of chromosomes. In normal sexual reproduction, the offspring get one set of
chromosomes from each parent, so this means that haploid spores only have genes from a single
parent, making them genetically identical to that parent. This haploid spore is dispersed by the parent
fungus and won't germinate until it lands in favorable growing conditions. But once it does, it already
has everything it needs to grow into a full, functioning adult fungus.
The vast majority of fungi reproduce asexually with haploid spores. However, a few unicellular fungi like
yeast have a different form of asexual reproduction. Budding, in which part of the cell divides creating a
new individual, is the other way that a few fungi can asexually reproduce. Part of the parent cell divides,
creating a bud (a genetic clone that will eventually grow into an adult cell), and when it does, detaches
itself from the parent.
Sexual Reproduction
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03/05/2021
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Now, it's pretty cool that fungi can just clone themselves, but this is not a viable long-term evolutionary
practice. Eventually, you need some genetic diversity so the species can adapt and evolve. So, sexual
reproduction is also important. This happens by fusing together different haploid hyphae, long, thin
cells that form filaments that make up the fungus' body. A group of hyphae is called a mycelium, and
sexual reproduction begins when two mycelium fuse together. This stage is called plasmogamy, when
two haploid hyphae merge into one, resulting in a single cell with two nuclei. After this occurs, the new
cell enters the stage of karyogamy, and the two nuclei fuse into one.
So, now this cell has a single nucleus but two sets of chromosomes, one from each parent, making it a
diploid cell. From here, the cell undergoes meiosis, cell division reducing the number of chromosomes
back to a single set. Finally, we have a haploid cell with a single set of chromosomes that is genetically
different from the parent. This then becomes a spore and is dispersed into the world.
Lesson Summary
Not many organisms have a choice when it comes to how to produce offspring. However, fungi,
nonphotosynthetic organisms that decompose food before absorbing it, do. Most fungi can reproduce
both sexually, requiring two parents to mix genes, and asexually, with only one parent.
For the most part, reproduction involves creating spores, tiny reproductive units which are sort of like
seeds but are smaller and lighter. Asexual reproduction occurs when haploid spores, spores with one
set of chromosomes, are released by the fungus. Once these spores germinate, they will create an adult
that is genetically identical to the parent.
However, most fungi can also reproduce sexually by fusing together haploid hyphae, long, thin cells
that form filaments that make up the fungus' body. This starts with plasmogamy, as two haploid
hyphae merge into one, resulting in a single cell with two nuclei. Next comes karyogamy, when the two
nuclei fuse into one. From here, the cell undergoes meiosis, cell division reducing the number of
chromosomes back to a single set, creating a spore that is genetically different from the parent. So,
that's how fungi reproduce. No stork needed.
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