Sasha (Alexandra) Khristich
@khristich.bsky.social
postdoc at the Petrov lab at Stanford studying evolution & evolvability
Is it possible that the fact that AMA is a triploid is related to its apparent higher evolvability? We don’t know. But it’s fun to speculate that maybe a heterozygous triploid has access to more haplotype combinations it can convert to, and is able to fine-tune allele dosage.
September 22, 2026 at 6:34 PM
Is it possible that the fact that AMA is a triploid is related to its apparent higher evolvability? We don’t know. But it’s fun to speculate that maybe a heterozygous triploid has access to more haplotype combinations it can convert to, and is able to fine-tune allele dosage.
We also noticed that some of the tracts localized in the same place across different strains, like these tracts from strains evolved in M3 and M3-5GLU media (here each line is an LOH event from one strain and colors separate independent isolates):
September 22, 2026 at 6:34 PM
We also noticed that some of the tracts localized in the same place across different strains, like these tracts from strains evolved in M3 and M3-5GLU media (here each line is an LOH event from one strain and colors separate independent isolates):
Third interesting observation: CCV and CGB both started with lower fitness than BBK, but CCV stuck around for about 60 transfers (until it eventually died out), and CGB rose to high frequency in one replicate:
September 22, 2026 at 6:34 PM
Third interesting observation: CCV and CGB both started with lower fitness than BBK, but CCV stuck around for about 60 transfers (until it eventually died out), and CGB rose to high frequency in one replicate:
Second interesting observation: BBK was the 5th fittest strain but did not persist at measurable frequency even until the 23rd transfer:
September 22, 2026 at 6:34 PM
Second interesting observation: BBK was the 5th fittest strain but did not persist at measurable frequency even until the 23rd transfer:
First interesting observation: AMA and BFB had approximately the same fitness. Despite BFB starting with a slightly higher frequency, AMA ended up more common in the final pool composition! In AMA’s and BFB’s trajectories across replicates, we can see when adaptive mutations arise:
September 22, 2026 at 6:34 PM
First interesting observation: AMA and BFB had approximately the same fitness. Despite BFB starting with a slightly higher frequency, AMA ended up more common in the final pool composition! In AMA’s and BFB’s trajectories across replicates, we can see when adaptive mutations arise:
Zooming in on the final average frequencies of the finalists in M3, we noticed that for the fittest 5% of strains, initial fitness was not a great predictor of long-term success (here, finalists are colored and other strains from the top 5% are white):
September 22, 2026 at 6:34 PM
Zooming in on the final average frequencies of the finalists in M3, we noticed that for the fittest 5% of strains, initial fitness was not a great predictor of long-term success (here, finalists are colored and other strains from the top 5% are white):
And in M3 (minimal glucose-limited media), we saw a combination of coexistence and alternative states:
September 22, 2026 at 6:34 PM
And in M3 (minimal glucose-limited media), we saw a combination of coexistence and alternative states:
In SC-HU (synthetic complete media with hydroxyurea), there seemed to be several alternative states where one of three strains dominated in different replicates:
September 22, 2026 at 6:34 PM
In SC-HU (synthetic complete media with hydroxyurea), there seemed to be several alternative states where one of three strains dominated in different replicates:
For example, looking at the population composition at the last timepoint of M3-5GLU (minimal media with excess glucose) replicates, we observed possible long-term coexistence among several strains:
September 22, 2026 at 6:34 PM
For example, looking at the population composition at the last timepoint of M3-5GLU (minimal media with excess glucose) replicates, we observed possible long-term coexistence among several strains:
So that’s what we did! We pooled our strains and grew them in batch culture for up to 700 generations (90 2-day transfers) in 6 different media types and in up to 20 replicates per media. You can think of this experiment as a yeast ‘survivor’ game repeated many times.
September 22, 2026 at 6:34 PM
So that’s what we did! We pooled our strains and grew them in batch culture for up to 700 generations (90 2-day transfers) in 6 different media types and in up to 20 replicates per media. You can think of this experiment as a yeast ‘survivor’ game repeated many times.
* We can then propagate them for a longer time and see which strain wins in the end. And by running many replicates, we can quantitatively estimate the chances of long-term success for each strain:
September 22, 2026 at 6:34 PM
* We can then propagate them for a longer time and see which strain wins in the end. And by running many replicates, we can quantitatively estimate the chances of long-term success for each strain:
What makes this collection great for our experiment:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
September 22, 2026 at 6:34 PM
What makes this collection great for our experiment:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
Is it possible that the fact that AMA is a triploid is related to its apparent higher evolvability? We don’t know. But it’s fun to speculate that maybe a heterozygous triploid has access to more haplotype combinations it can convert to, and is able to fine-tune allele dosage.
September 22, 2026 at 6:13 PM
Is it possible that the fact that AMA is a triploid is related to its apparent higher evolvability? We don’t know. But it’s fun to speculate that maybe a heterozygous triploid has access to more haplotype combinations it can convert to, and is able to fine-tune allele dosage.
We also noticed that some of the tracts localized in the same place across different strains, like these tracts from strains evolved in M3 and M3-5GLU media (here each line is an LOH event from one strain and colors separate independent isolates):
September 22, 2026 at 6:13 PM
We also noticed that some of the tracts localized in the same place across different strains, like these tracts from strains evolved in M3 and M3-5GLU media (here each line is an LOH event from one strain and colors separate independent isolates):
Third interesting observation: CCV and CGB both started with lower fitness than BBK, but CCV stuck around for about 60 transfers (until it eventually died out), and CGB rose to high frequency in one replicate:
September 22, 2026 at 6:13 PM
Third interesting observation: CCV and CGB both started with lower fitness than BBK, but CCV stuck around for about 60 transfers (until it eventually died out), and CGB rose to high frequency in one replicate:
Second interesting observation: BBK was the 5th fittest strain but did not persist at measurable frequency even until the 23rd transfer:
September 22, 2026 at 6:13 PM
Second interesting observation: BBK was the 5th fittest strain but did not persist at measurable frequency even until the 23rd transfer:
First interesting observation: AMA and BFB had approximately the same fitness. Despite BFB starting with a slightly higher frequency, AMA ended up more common in the final pool composition! In AMA’s and BFB’s trajectories across replicates in M3, we can see when adaptive mutations arise:
September 22, 2026 at 6:13 PM
First interesting observation: AMA and BFB had approximately the same fitness. Despite BFB starting with a slightly higher frequency, AMA ended up more common in the final pool composition! In AMA’s and BFB’s trajectories across replicates in M3, we can see when adaptive mutations arise:
Zooming in on the final average frequencies of the finalists in M3, we noticed that for the fittest 5% of strains, initial fitness was not a great predictor of long-term success (here, finalists are colored and other strains from the top 5% are white):
September 22, 2026 at 6:13 PM
Zooming in on the final average frequencies of the finalists in M3, we noticed that for the fittest 5% of strains, initial fitness was not a great predictor of long-term success (here, finalists are colored and other strains from the top 5% are white):
And in M3 (minimal glucose-limited media), we saw a combination of coexistence and alternative states:
September 22, 2026 at 6:13 PM
And in M3 (minimal glucose-limited media), we saw a combination of coexistence and alternative states:
In SC-HU (synthetic complete media with hydroxyurea), there seemed to be several alternative states where one of three strains dominated in different replicates:
September 22, 2026 at 6:13 PM
In SC-HU (synthetic complete media with hydroxyurea), there seemed to be several alternative states where one of three strains dominated in different replicates:
For example, looking at the population composition at the last timepoint of M3-5GLU (minimal media with excess glucose) replicates, we observed possible long-term coexistence among several strains:
September 22, 2026 at 6:13 PM
For example, looking at the population composition at the last timepoint of M3-5GLU (minimal media with excess glucose) replicates, we observed possible long-term coexistence among several strains:
So that’s what we did! We pooled our strains and grew them in batch culture for up to 700 generations (90 2-day transfers) in 6 different media types and in up to 20 replicates per media. You can think of this experiment as a yeast ‘survivor’ game repeated many times.
September 22, 2026 at 6:13 PM
So that’s what we did! We pooled our strains and grew them in batch culture for up to 700 generations (90 2-day transfers) in 6 different media types and in up to 20 replicates per media. You can think of this experiment as a yeast ‘survivor’ game repeated many times.
* We can then propagate them for a longer time and see which strain wins in the end. And by running many replicates, we can quantitatively estimate the chances of long-term success for each strain:
September 22, 2026 at 6:13 PM
* We can then propagate them for a longer time and see which strain wins in the end. And by running many replicates, we can quantitatively estimate the chances of long-term success for each strain:
What makes this collection great for our experiment:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
September 22, 2026 at 6:13 PM
What makes this collection great for our experiment:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
* It contains yeast strains collected worldwide from different ecological niches (bakeries, wineries, breweries, flowers and trees, insects’ guts, etc.), and is a good proxy for the species’ overall diversity:
Is it possible that the fact that AMA is a triploid is related to its apparent higher evolvability? We don’t know. But it’s fun to speculate that maybe a heterozygous triploid has access to more haplotype combinations it can convert to, and is able to fine-tune allele dosage.
September 22, 2026 at 5:44 PM
Is it possible that the fact that AMA is a triploid is related to its apparent higher evolvability? We don’t know. But it’s fun to speculate that maybe a heterozygous triploid has access to more haplotype combinations it can convert to, and is able to fine-tune allele dosage.