| Method |
"The fact that no synonymous mutations fixed in the first 20,000
generations is consistent with the low point-mutation rate in
E. coli
and population-genetic theory if those mutations are selectively
neutral. According to theory, the expected rate of neutral substitutions equals the rate of neutral mutations
[ref 12]
. [Researchers] calculate an upper
bound for the mutation rate from the Poisson distribution, which
specifies a 5% chance that no synonymous substitutions would occur
even if three were expected. That upper bound corresponds to a
mutation rate of 1.6×10^-10
per bp per generation given 20,000
generations, a genome length of 4.63×10^6
bp, and the fact that
20.4% of all possible point mutations are synonymous." |