We humans are used to using the XX/XY chromosomes to determine which sex we belong to. If you have two X chromosomes, you are a female, while you are a male if you have one X chromosome and one Y chromosome. However, if you were a bird you would need two Z chromosomes to be a male, while a female bird will have one Z chromosome and one W chromosome. This is still straight forward, but once we get to mushrooms, things get a bit more complicated to say the least.
An image of the human sex chromosomes. X is the big one on the left, and the small one on the right is the Y. This means it is XY, so it is from a male. Image by National Human Genome Research Institute, posted as Public Domain.
You can find more than 4,000 sexes in mushrooms
In the phyla called Basidiomycota within fungi, we can find incredibly many types of sexes, known as mating types. A mushroom can create fertilized offspring with any another mating type, but not the same as the one it is. The reason as to why it cannot mate with its own type is to prevent selfing, an event where the mushroom would fertilize itself.
Basidiomycota is a phylum that consists of most of the mushrooms we pick when we are in the forest, with a few exceptions. The exceptions, such as true morels (Morchella ssp) all belong in the phylum Ascomycota, which do not have this high amount of mating types (in fact, they only have two, and are in a sense more relatable to animals).
One of the very many fungi that belongs to the Basidiomycota phylum. Most of the common mushrooms belong in this phulym. Image by Scott Darbey, posted with the Creative Commons Attribution 2.0 Generic license.
Why mushrooms has so many mating types
There is actually a somewhat simple explanation as to why the mushrooms can have so many different mating types, while most other organisms only have a few. As I said in the introduction, most organisms have their sex determined by their chromosomes. In Basidiomycota, it works on a very different level. The mating types are not decided by a whole chromosome, and instead by a few genes. There a known cases of four different genes that decide the mating type, with several different alleles for each gene.
In the phylum of Ascomycota there are only two mating types, but these are also determined by a single gene, not by several of them.
Trying to explain it a bit easier
What does this mean? An allele is one possible variation of a gene sitting on a locus in a chromosome. The higher amount of the alleles, the more variation will be found in the mushroom, which in this case will mean a higher amount of different possible mating types. If there are few alleles for a trait, there will be little variation of the things the alleles code for.
Try to think of it as hair color in humans. This is not decided by a whole chromosome, but instead by a combination of genes. If you have alleles to have blonde hair, this will be reflected in your phenotype (the physical appearance*), just like the mating type will be determined by the alleles in mushrooms.
The thing to take away from this post is that the sexes in Basidiomycota is determined by two, three or even four different genes, not by a whole chromosome. This opens up the opportunity to have many different sexes / mating types, because there are so many different gene combinations for these.
*Phenotype is used when we are talking about the physical appearance of an organism, but using the term physical appearance is not 100 % correct, since a few more features would be included in the phenotype. However, for non-biologist, think of phenotypes as the physical appearance of the organism.
Thanks for reading
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Understanding mating systems in mushrooms is pretty difficult, and it is a very complex system, so some of my information might be a little wrong, and it certainly does not explain all of it. However, I hope you enjoyed this little taste of how mating types functions in the Basidiomycota. Check the sources below if you are interested to learn more about the mating types in mushroom.
Sources
- Mate recognition in fungi, by L A Casselton, Heredity (2002) 88, 142–147. DOI: 10.1038/sj.hdy.6800035. This is a scientific paper written about mate recognition, which also includes some info about the mating types. This can be pretty difficult to understand for people who don’t really know a lot about fungi.
- The Wikipedia page on Mating in fungi also has lots of information, but this is also pretty complicated to read for people who are not familiar with fungi.
- Not used as a source, but check out the Wikipedia page on alleles to better understand them.
Mushroom-Monday
This post is part of a project I started, called #Mushroom-Monday. I plan to post about mushrooms every Monday, and I want as many people as possible to join me! Today I’m also giving away some STEEM to people who join me, so check out my post about Mushroom-Monday by clicking here.