Posted by: Kay at Suicyte | October 4, 2007

Gender issues (fungal)

This is a kind of follow-up to my previous post “Try to explain this to a non-biologist“, where I was making fun of yeast mating type nomenclature.

Through a recent posting on Fungal Genomes (and a number of random clicks that I am unable to reproduce), I eventually found a page written by Tom Volk, explaining fungal sex using Schizophyllum commune as an example. I must say that I learned a lot by reading this page (I am often exposed to sequence data from various fungi, typically without having a good idea about their basic biological features and differences). One of the more amazing facts is that Schizophyllum comes in more than 28,000 different mating types. There was one paragraph, though, that reminded my immediately of my former “a vs. α” problem:

Many of the more primitive fungi have only two sexes. In some cases we can distinguish male from female gametes or gametangia, but in most cases they are morphologically identical. In these cases we must call them + and -, or A and a, or 1 and 2.

Wait a second. I have no problems with calling them “+ and -“, we do the same with opposite charges. Also, “1 and 2” is not a big deal (although my friends from computer science maintain that “0 and 1” would be preferable). But why would anybody go for “A and a”? How are we supposed to find the difference in a pubmed search? And, what is wrong with plain old “A and B”?

The text goes on, explaining that in some fungi, mating type loci can carry more than two different alleles. It is plain to see that both the “+ vs. -” and the “A vs. a” systems don’t scale very well with the number of alleles. And I haven’t even started on this α thing.

Who knows, maybe one day they will be a new fungal species and call the two mating types “A” and “Frederic”. For purely historical reasons, obviously.

Post scriptum: I will be on vacation until October 12, far away from any nternet connection, in the northwestern region of beautiful Sardinia (should have stayed in Italy after the ubiquitin meeting!)



  1. Well in the tetrapolar mating systems in some fungi including many basidiomycetes from the corn smut Ustilago maydis to the mushrooms Coprinus cinereus and Schizophyllum there are two loci that control mating type. So called A and B loci and each can have a different allele and are unlinked and independently segregate. There are several good reviews on this – I think you have probably inspired us to write up a post on it.

    Also have a look at how a bipolar (A or alpha, + or -) mating system can evolve from a tetra-polar system when the A and B loci become physically linked from a nice paper on Cryptococcus MAT locus evolution Fraer et al, PLoS Biology 2004

  2. I kinda like the A and alpha, if it weren’t for having to deal with greek letters in Pubmed. It certainly emphasizes the parallelism of the downstream pathways.

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