Molecular Characterization of Clonal Interference during Adaptive Evolution in Asexual Populations..

..of Saccharomyces cerevisiae
Gavin Sherlock
Afternoon Session, 1 September (11th MGED Meeting, 1-4 September, 2008)

The population structure in the presence of clonal interference is markedly different from that in a classic model. They needed a system to model population dynamics in a population. They use FACS and different-colored fluorescent cells to do this. They grew the cells in a chemostat, which is seeded with equal numbers of each of the 3 color types, and then measure the proportion of the population over time. The experiment has been done 8 different times. One run, for example, shows expansions and contractions followed by one color becoming the majority. Fixation of a color is not necessarily indicative of fixation of an adaptive event (multiple adaptive clones within a population with the same color).

Using yeast tiling microarrays, they can identifiy location nucleotide differences between the evolved and parent strains. Then sequence the candidate mutations. One of the mutations they found (in cox18) called Red 266 was discovered via decreased hybridization compared to the parent. Another example was where there was a comparatively higher level of hybridization. Mutation history can help determine which strains come from which earlier parent strains with mutations of their own.

Clonal interference is important in adaptive evolution of yeast. Specifically, glucose transport and signalling through the Ras pathway were both affected. In future, they wish to directly determine which mutations are adaptive, find out how general these adaptations are, and discover the effects of the adaptive mutations, and finally - what fraction of the adaptive landscape have we explored? Will it be the same or different in the other 7 experiments?

These are just my notes and are not guaranteed to be correct. Please feel free to let me know about any errors, which are all my fault and not the fault of the speaker. :)