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Timothy McDougald



Posts: 1008
Joined: Dec. 2006

(Permalink) Posted: Jan. 18 2012,15:55   

Based on this bit from the PNAS article:

Quote
We used gravity to select for primitive multicellularity in the unicellular yeast Saccharomyces cerevisiae. Clusters of cells settle through liquid more quickly than do single cells, allowing us to easily select for clustering genotypes. Settling selection was chosen not because it is widespread in nature, but rather because it is an experimentally tractable method to select for larger size.Ten replicate populations of initially isogenic S. cerevisiae were grown in nutrient-rich liquid medium with shaking to stationary phase (?109 cells/replicate population) before subculturing and daily transfer to fresh medium. All replicate populations were allowed to stand for 45 min before transfer to 10 mL fresh medium, during
which time cells settled toward the bottom of the culture tube. Cells in the lower 100 ?L were then transferred to fresh medium. After the first week, we modified the settling step to be more time efficient by using 100 g, 10-s centrifugations of 1.5-mL subsamples from the shaken 10-mL tube to settle population fractions for transfer to fresh medium. We expected these conditions to select for clusters of cells, whether by postdivision adhesion or by aggregation.


A case could be made that it was natural selection, although it does seem kind of borderlinish to so describe it.

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