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Old 02-20-2011, 05:30 PM   #1
winnph
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Default Crossing yeast strains

So I know very little about yeast biology, but my understanding is that yeast can undergo both asexual (budding) reproduction and sexual (spores combining) reproduction. My understanding is also that yeast in ordinary brewing is almost exclusively budding asexually, so if you blend more than one strain, they will be competing rather than mating. Eventually one strain dominates, and it basically has the properties that strain would have had if you'd just pitched it alone.

What I'm curious about is sexual reproduction.... Is there any way a homebrewer can get two yeast strains to release spores, combine those spores, and therefore produce a hybrid strain? In other words, is there an easy way to induce sexual reproduction in yeast, and to capture the product of that reproduction and step it up for brewing purposes? Also, does this happen to some extent when you blend yeast, or are the strains exclusively budding at that point?

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Old 02-20-2011, 05:45 PM   #2
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From the PhD Microbiologist on my couch, yeast do not produce sexually "because they are single-cellular organisms." Spore production is asexual reproduction.

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Old 02-20-2011, 05:50 PM   #3
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http://en.wikipedia.org/wiki/Yeast#Reproduction

So Wikipedia lies?

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Old 02-20-2011, 05:54 PM   #4
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Ha. She's wrong. I love it.

To answer the other question, yes Wikipedia does lie. Though, not in this case it seems.

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Old 02-20-2011, 06:08 PM   #5
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Ah yes, I don't doubt that Wikipedia has many a lie lurking uncaught by its vigilante editors. They always seem to undo anything I change, even when I know it was worthwhile (like fixing typos), so I've long since given up on contributing or editing.

So, back to my original question... does anyone know how to induce sexual reproduction in two strains, and control the process well enough to cause them to produce a hybrid strain "offspring"?

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Old 02-20-2011, 06:28 PM   #6
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Not going to happen, these strains have been so mutated over the years that any sexual reproduction would start you off at square 1. You would terrible yeast charecteristics for many hundred of generations until you refined it enough.

And given the fact that it is not known how Saccaromyces cerevisiae originated (hybridized with wine yeast c. 400 years ago?) you could end up with something not even similar to S. cerevisiae.

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Old 02-20-2011, 06:40 PM   #7
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Quote:
Originally Posted by theredben View Post
Not going to happen, these strains have been so mutated over the years that any sexual reproduction would start you off at square 1. You would terrible yeast charecteristics for many hundred of generations until you refined it enough.

And given the fact that it is not known how Saccaromyces cerevisiae originated (hybridized with wine yeast c. 400 years ago?) you could end up with something not even similar to S. cerevisiae.
I'm not sure I see how two S. cerevisiae strains, when combined, would be expected to produce anything wildly different from the parent strains. I mean, I would guess that most yeast strains are still fairly closely related, other than a few outliers (that species used in German wheat beers, for example). Also, it seems from what I've read that S. cerevisiae does undergo a sexual reproductive cycle fairly regularly, so wouldn't some minimal degree of cross-breeding be occurring every time you use a blended yeast, like WLP575, for example?

But really the point isn't that I expect the product will be great, but rather I wish to experiment with this process to see what the product will be. My favorite part of brewing is tinkering and trying new things even when they have a decent chance of ending badly.
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Old 02-20-2011, 06:43 PM   #8
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I would have thought Yeast were only asexual. However I did a google search for 'yeast mitosis meiosis' and found a lot of hits. Like these:

"Using Saccharomyces cerevisiae to study cell cycle genes in meiosis"
Anne Galbraith, Dept of Biology, University of Wisconsin-La Crosse

Quote:
Finally, although yeast does not look anything like a human, it still grows and divides by the processes of mitosis and meiosis.
Comparative sensitivity to gamma radiation of yeast mitosis and meiosis
J.J. Millera, V.V. Kingsley*, a and C. Ramirez†, a
aDepartment of Biology and Research Unit for Biochemistry, Biophysics and Molecular Biology, McMaster University, Hamilton, Canada

Induction of meiosis in yeast
A. F. Croes


So there just may be some truth to sex in the fermenter.
My faith in wikipedia has been restored ... for now.
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Old 02-20-2011, 06:51 PM   #9
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My point is that when dealing with a highly refined asexually propogated organism (many plants, and our faithful brewing yeast) and then allowing sexual reproduction, the genetic transfer will allow it to revert back to some sembelance of that organism's original, uncultivated state. Crossing two strains is going to be impossible unless you have access to equipment to isolate individual cells. Otherwise, just putting two packets of yeast in a flask will inevitably end up with the sexual reproduction happening within the same strain as one will be stressed to the breaking point before the other.

But if you just want to play around, then I say go for it. Do you have access to a quality microscope? If you are going to stress the yeast to it's breaking point you will need some way to assure that what remains when all the haploid cells die off is still Saccaromyces cerevisiae.

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Old 02-20-2011, 07:05 PM   #10
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Yes, you can induce sexual reproduction in yeast, of course. It's a completely standard part of yeast genetics. It's possible it will be slightly harder in brewing strains, but I doubt it. It will be very difficult (practically speaking, impossible) to do so in any systematic way without a tetrad dissection microscope, and although it can be done in an entirely unsystematic way without one, I can't think of any way you could separate the progeny from the parental strains.

Contrary to what has been said above, there's no reason to think it would "revert" to an "uncultivated" state. That is not (thankfully for the field of genetics) how crosses generally work out.

In summary: Yes, it would be fairly easy given the correct equipment, yes, you'd probably be able to get something like a mixture of the two, but no, it would be very challenging for someone without expensive equipment and a background in microbiology.

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