Weakened selection and shifting patterns of polymorphism in Shigella
Speaker: Edward Feil
Dept Biology and Biochemistry, University of Bath
Most de novo mutations are neither advantageous to the bacterium, nor excessively harmful, but are instead slightly deleterious. Most of these mutations will be removed from the population by purifying selection, but this process takes time. The efficiency of selection depends upon the selective coefficient, s, and the effective population size, Ne. In small populations, such as those corresponding to an ecological “island”, selection is relatively inefficient and deleterious mutations accumulate. Here I will discuss the implications of this process, and will present an comparative analysis of E. coli and Shigella to illustrate how examining polymorphism frequencies provides a far more sensitive test for the efficiency of selection than analyses of base composition.