New evidence from a study of yeast cells has resulted in the most detailed picture of an organism's evolutionary process to date, says a Texas A&M University chemical engineering professor whose findings provide the first direct evidence of aspects, which up until now have remained mostly theory.
Working with populations of yeast cells, which were color-coded by fluorescent markers, Katy Kao, assistant professor in the Artie McFerrin Department of Chemical Engineering, and Stanford University colleague Gavin Sherlock were able to evolve the cells while maintaining a visual analysis of the entire process.
Their research, which appears in the December edition of Nature Genetics, shows the evolutionary process to be much more dynamic than initially thought, with multiple beneficial adaptations arising within a population. These adaptations, Kao explained, triggered a competition between these segments, known as "clonal interference."
It's the first direct experimental evidence of this phenomenon in eukaryotic cells, or cells with nuclei, and it contrasts the widely accepted classical model of evolution, which doesn't account for simultaneously developing beneficial adaptations, she said. Instead, that model adopts a linear approach, theorizing that a population acquires such adaptations successively, one after another. Rather than a competition occurring, the model posits a complete replacement of one generation by another better-adapted generation.
That wasn't the case in Kao's sample.
Observing the color-coded yeast populations as they evolved to respond to their environment, Kao saw some colors expand while others contracted a sign that adaptations were occurring. But rather than one segment of the population continuing to shrink until it was completely replaced, some segments were able to compete long enough to acquire further adaptations. When this happened, Kao explained, these populations of cells once apparently less-fit began
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Texas A&M University