Is multiple paternity necessary for the evolution of genomic imprinting?

GENOMIC imprinting, the inactivation of one allele will be growth promoters and maternally expressed ones growth suppressors (or more generally enhancers of the dependent upon the sex of the parent from which it was derived, has understandably generated considerindividual’s fitness and suppressors of the individual’s fitness, respectively). In a recent article, however, Spenable interest from theoretical evolutionary biologists. Selection should favor diploid (biallelic) expression to cer et al. (1998) closely analyze diallelic population genetic models for the evolution of genomic imprinting protect against spontaneous deleterious recessive mutations, so the fact that some genes are haploid (monoaland come to different conclusions. They find that multiple paternity is not a necessary requirement and that lelically) expressed clearly requires explanation (Hurst 1997). the correspondence between growth effect and imprint direction does not always hold. The most frequently discussed hypothesis for the evolution of imprinting (but by no means the only one, see The discrepancies between the models have been asserted by both sides of the debate to be a consequence for review Hurst 1997) is the so-called conflict model (Moore and Haig 1991). The premise of this hypothesis of a difference in the class of models employed. Additionally, Spencer et al. argue that their diallelic models is that under multiple paternity a rare paternally derived allele has a lower probability of being in other progeny have the advantage of explicitly analyzing the transition from the unimprinted to the imprinted state rather than of the same mother than does a comparably rare maternally derived allele in the same fetus (assuming the rare simply looking for a stable state. They therefore consider the conclusions of the other models to be restrictive alleles were inherited). As a consequence, should the paternally derived allele be able to direct resources to(see also Spencer et al. 1999). In reply, however, Haig (1999) argues that diallelic models are limited to considward the embryo containing it, then it is more likely to spread than a maternally derived allele doing the same. ering only the fate of the alleles in question and hence are not appropriate for considering what happens to This is because the maternally derived allele’s fitness is in part the fitness of other progeny, whereas the patersuch a population in the longer term when subjected to different alleles. He concludes that it is therefore nally derived allele’s fitness will not be reduced by the mother’s reduced production of other progeny. The Spencer et al.’s models that are misleading. Here I address the issue of whether diallelic models maternal and paternal alleles are hence under different selection pressures and this difference is hypothesized can be appropriate to address this problem and whether by necessity diallelic and game theoretical models will to explain why some genes are inactive when maternally inherited (putative growth enhancers) and others are disagree. I show that the differences between Haig’s and Spencer et al.’s conclusions are not owing to a differinactive when paternally derived (putative growth supence in the class of models used. Instead, the discrepancpressors). Under monogamy, the paternally derived alies stem from Spencer et al.’s restricted application of lele suffers and gains every bit as much by the effects diallelic models. When one uses diallelic models to adon other progeny as does a maternally derived allele dress the issue of the persistence of imprinting, as well and so imprinting is not expected. as its initial evolution, the results conform with those Two early models, one game theoretical (Haig 1992) of the earlier models. I start, however, by exploring and one applying evolutionarily stable strategy (ESS) more fully Spencer et al.’s models so as to highlight theory to a quantitative genetical model (Mochizuki et their limitations. al. 1996), have supported the verbal model and confirm the predictions that multiple paternity is necessary for imprinting to evolve and that paternally expressed genes IMPRINTING WITHOUT SIB COMPETITION