  This paper develops a two gene, single fitness peak model for determining the
equilibrium distribution of genotypes in a unicellular population which is
capable of genetic damage repair. The first gene, denoted by $ \sigma_{via} $,
yields a viable organism with first order growth rate constant $ k > 1 $ if it
is equal to some target ``master'' sequence $ \sigma_{via, 0} $. The second
gene, denoted by $ \sigma_{rep} $, yields an organism capable of genetic repair
if it is equal to some target ``master'' sequence $ \sigma_{rep, 0} $. This
model is analytically solvable in the limit of infinite sequence length, and
gives an equilibrium distribution which depends on $ \mu \equiv L\eps $, the
product of sequence length and per base pair replication error probability, and
$ \eps_r $, the probability of repair failure per base pair. The equilibrium
distribution is shown to exist in one of three possible ``phases.'' In the
first phase, the population is localized about the viability and repairing
master sequences. As $ \eps_r $ exceeds the fraction of deleterious mutations,
the population undergoes a ``repair'' catastrophe, in which the equilibrium
distribution is still localized about the viability master sequence, but is
spread ergodically over the sequence subspace defined by the repair gene. Below
the repair catastrophe, the distribution undergoes the error catastrophe when $
\mu $ exceeds $ \ln k/\eps_r $, while above the repair catastrophe, the
distribution undergoes the error catastrophe when $ \mu $ exceeds $ \ln
k/f_{del} $, where $ f_{del} $ denotes the fraction of deleterious mutations.
