  Fontanari et al introduced [Phys. Rev. Lett. 91, 218101 (2003)] a model for
studying the Muller's ratchet phenomenon in growing asexual populations. They
studied two situations, either including or not a death probability for each
newborn, but were able to find analytical (recursive) expressions only in the
no-decay case. In this paper a branching process formalism is used to find
recorrence equations that generalize the analytical results of the original
paper besides confirming the interesting effects their simulations revealed.
