Saccharmoyces cerevisiae and sex

Ah, yeast. That beautiful, single-celled organism that gives us so much good stuff–mmm…beer. Well, at them moment, the GRE doesn’t seem to care about the goodness of alcohol. Instead, it cares more about the taxonomical groupings of the yeast responsible for some many drunken hookups–Saccharomyces cerevisiae.

Here’s the question:

The yeast Saccharomyces cerevisiae is classified as belonging to which of the following groups?

A) Eubacteria
B) Oomycota
C) Zygomycota
D) Ascomycota
E) Basidiomycota

Scientists like grouping like things together. We don’t like having all these uncategorized species just lying around all on their own. Who do they think they are?!? Anyhow, S. cerevisiae is a yeast. Yeasts are a type of fungus, and are grouped together with all those fungi you know and love–mushrooms and molds. Members of the fungal group are put together by their method of sexual reproduction.

Ok, so fungi reproduce by producing spores–hardy, thick walled thingys that can survive most any horrible thing. Most molds reproduce most of the time asexually. This takes less effort and energy than sexual reproduction, so it tends to be the go-to option for most species. When times get rough, however, almost all of the species resort to sex to make sure their offspring have a good chance of survival.

So, what “groups” do fungi fall into? There are 6 major fungal groups (specifically, they are phyla): Chytridiomycota, Oomycota, Zygomycota, Ascomycota, Deutromycota, and Basidiomycota. Notice that all the fungal groups end in -mycota (that’s a big clue to this question). The Chytrids are ancient molds, mostly aquatic, and super interesting to other people. The big representative of this group is Allomyces.

The second group is Oomycota, which are filamentous, water and downy mildew molds. As all of you who know a little bit about beer and bread, S. cerevisiae is a single celled organism, so it doesn’t fall into Oomycota.

The final three groups are the higher fungal groups, and our best bet for S. cerevisiae. Organisms in Zygomycota produce zygospores; those in Ascomycota produce ascospores within an ascus; Basidiomycota members produce basidiospores; and organisms in Deutromycota don’t have any known sexual cycle. Granted, that last group is just a catch-all for all the organisms we’ve discovered that we can’t make do it in the lab.

Well, what do S. cerevisiae do? They produce ascospores within an ascus. I really don’t have a good way of helping you remember this–maybe just straight memorization here? Sorry!

So, back to our question:

The yeast Saccharomyces cerevisiae is classified as belonging to which of the following groups?

A) Eubacteria
B) Oomycota
C) Zygomycota
D) Ascomycota
E) Basidiomycota

As we now know, Saccharomyces cerevisiae belongs to Ascomycota. Yay!

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