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 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)
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