We introduce a model of molecular evolution in which the fitness of an individual depends both on its own and on the parent's genotype. The model can be solved by means of a nonlinear mapping onto the standard quasispecies model. The dependency on the parental genotypes cancels from the mean fitness, but not from the individual sequence concentrations. For finite populations, the position of the error threshold is very sensitive to the influence from parent genotypes. In addition to biological applications, our model is important for understanding the dynamics of self-replicating computer programs.PACS numbers: 87.23.KgSimple models of asexual evolution, such as the quasispecies model, typically assume that the fitness of an organism is a function of only its genotype and the environment. This allows for the analysis of evolution in static [1][2][3][4][5][6][7] or variable [8][9][10] environments, many to one mappings from genotype to phenotype (neutrality) [11][12][13], and phenotypic plasticity [14]. These models disregard the potential influence of the mother (or parent, in general) on the organism's phenotype. This influence comes about because in addition to the genetic material, a wealth of proteins and other substances is transferred from mother to child. In the context of sexual reproduction, the influence of the mother on a child's phenotype is usually called a maternal effect. A classic example is that of the snail Partula suturalis [15], for which the directionality in the coiling of the shells is determined by the genotype of the mother of an organism, rather than the organism's own genotype. Maternal effects are not exclusive to sexually reproducing organisms, however, they can be observed in simple asexual organisms as well. In bacteria, for example, the fitness of a strain in a given environment may depend on the environment that was experienced by the strain's immediate ancestors [16,17].Here, our objective is to define and study a model of the evolution of asexual organisms that takes such maternal effects into account. We assume that the fitness of an organism is given by the product of two quantities a and b, where a depends solely on the genotype of the mother of the organism, and b depends solely on the organism's own genotype. Since we need to keep track of the abundances of all possible mother/child combinations, we need n 2 concentration variables if we distinguish n different genotypes in our model. In the following, we denote by x ij the concentration of organisms of genotype j descended from genotype i, and by q ji the probability that a genotype i mutates into genotype j. The time evolution of the x ij is then, in analogy to the quasispecies model,ẋ