Luria &
Delbruck Thought Experiment #1 : Induction
Each of four cultures is started with a
single bacterial cell. Each cell divides once per generation,
producing two cells. At the end of 4 generations, 15
cell divisions produce 24 = 16 cells in each culture, for a total of 64 cells.
In the final generation, each culture
is exposed to the phage. Most bacterial cells are sensitive
(black). However, ten
cells (3, 1, 5,
& 1 in the four
cultures) are observed to be resistant
(blue). If resistance was induced by exposure to bacteriophage,
and all cells have an identical chance of becoming resistant, then
each culture is expected to have an equal number of
resistant cells. If the average number of resistant cells per
culture is small, the observed fluctuation among cultures will
follow the Poisson
Distribution, for which the variance equals the mean.