Two strains of E. coli, A and B, are inoculated into a chemostat in equal proportions. After one generation, the frequency of strain B is 20%. Calculate the fitness of strain B relative to strain A. Show your work.
Fitness (w) is a survival rate of a phenotype (bacterial strain 1) relative to the maximum survival rate of another phenotype (bacterial strain 2) in population. The frequencies of E.coli strains (A and B) in the input population are 50% for each strain. After one generation the frequencies of strains are 80% (strain A) and 20% (strain B). Relative changes of the frequency after one generation are: strain A = 80%/50% = 1.6 strain B = 20%/50% = 0.4 The fitness of strain B relative to strain A: w = 0.4/1.6 = 0.25 Answer: 0.25