Sorry for the terrible pun, but l’m legit curious.
A friend and I were talking about how some sourdough mothers, pho broths, etc can literally be human generations old. Is it a “Ship of Theseus” kind of thing? Does the process of maintaining the mother prevent this by adding in new yeast? Do the many generations of yeast make different strains of yeast? Is there a concern that the many yeast generations could create undesirable modifications?
In: Biology
Most yeast cells reproduce asexually via mitosis. So the yeast cells are biologically identical to each other, meaning it should be the same even over human generation type spans. Obviously mutations can and will occur over that time, but functionally speaking you can safely assume a sourdough starter across multiple generations is the same starter the whole time.
There are some yeast cells that can form multicellular organisms with itself, but I don’t know if those would be the type of yeast cells used in starters and then passed down, like the context of your question. But regardless, that subset of yeast cells might have more room for variation and changing gradually over time, but I’m not an expert and I don’t want to speculate too much.
With pho, yeast isn’t really an issue since it’s a broth that is boiled regularly, which will kill the yeast.
In sourdough starters, it’s not genetically pure because there is yeast in the air. So if some yeast becomes disadvantaged compared to the yeast floating around, the yeast that’s floating around will land in the starter and out-compete it.
Yes, there are hundreds or thousands different strains of yeast. Mostly the differences are noticeable in the growth speed and the preferred temperature.
Biggest split is between brewer yeast and baker yeast groups,
because brewer yeasts were artificially selected for alcohol tolerance and converting more sugar into alcohol. But brewer yeast also breeds slower for more controlled fermentation process, while in baker one quick rise is preferable.
Some beer and winemakers care a lot that their wine is made with the specific strain they were cultivating to taste right, but they’re also huge snobs.
Yeast is single celled and just clones itself.
Over years it will evolve to be well- adapted to a sourdough mother.
The undesirable mutations are generally gonna die out.
Most of the time, Yeasts reproduce by budding – asexually; they just grow a new self and split off from it. Some of the yeasts divide by fission like bacteria – they split in half and make two equally sized but otherwise identical smaller yeasts.
They can reproduce sexually, but it’s less common. Remember, a yeast is just a single cell, and to reproduce sexually you have to have half your usual number of chromosomes – you go from being diploid, to haploid. What they do is they divide by meoisis into a little bundle of 4 cells in a ball called an Ascus. The cells in there have two “”sexes”, called mating types”, ‘a’ and ‘α’. You have to be opposite types to mate sexually.
They can then continue to live that haploid life for a while, reproducing by budding into more haploid yeasts. Then, at some point, two opposite type yeasts will encounter one another and combine their genes in sexual reproduction, and go back to being one diploid yeast.
You also get instances where the mother yeast mates immediately with the daughter yeast because yeast has a special gene that lets it switch mating types, so the daughter of an a turns into an α and mates with it’s mother.
So yes, your yeast is highly inbred, though remember that you’re dealing with an *absolutely massive* population of cells, so it’s more like “the population of Europe” level of inbreeding than “I married my cousin” inbred.
Your yeast in a sourdough is actually made of many many species and strains of yeasts. It’s been estimated that different strains only cross with each other [once every few tens of thousands of generations](https://www.nature.com/articles/ng1859)
Yeah, it’s absolutely possible. You can ask “Why is inbreeding actually bad?”… and it turns out there’s a good answer. It’s bad because it substantially increases the probability of natural errors in your genome getting expressed, thereby creating a child that will have a miserable life. Increased expected suffering of both the child and the care-takers, that’s why it’s bad.
So can that happen to yeast? You bet! One yeast cell could absolutely split into a partially defective yeast cell. It’s just that yeast doesn’t really do the whole “compassion” thing. The weak ones die. The strong ones split in half and eventually die. Yeast doesn’t care what comes out of it
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