Although you are right that the original fluctuation test results
of Luria and Delbruck showed a mutation rate of 1 in 3 x 10 -8
mutations per cell division in E. coli, this is not the case
for eukaryotes (for a quick review of Luria and Delbruck, see
Stent, GS; Molecular Genetics an Introductory Narrative, WH Freeman &
Co., 1978, pp 160-164).
The best guess there, with about 3 times 10 to the 9th base pairs of
DNA operative is that a single gene (containing about 10 to the 3rd base
pairs of coding sequence) would suffer a mutation once in every
million cell generations. (See Alberts, Bray, Lewis, Raff et al.,
Molecular Biology of the Cell, Garland, 1994, at page 243).
Bert Gold, Ph.D.