  We consider an exponentially growing population of cells undergoing mutations
and ask about the effect of reproductive fluctuations (genetic drift) on its
long-term evolution. We combine first step analysis with the stochastic
dynamics of a birth-death process to analytically calculate the probability
that the parent of a given genotype will go extinct. We compare the results
with numerical simulations and show how this turnover of genetic clones can be
used to infer the rates underlying the population dynamics. Our work is
motivated by growing populations of tumour cells, the epidemic spread of
viruses, and bacterial growth.
