Here, a two- loci mathematical model for the evolution of imprinting is hypothesized, in which imprinting of the alleles depends on the alleles of another loci, a cis- acting modifier. This paramutation- based model can explain either maternal or paternal inactivation.
we [... propose] that imprinting will evolve in situations in which selection favors offspring being similar to the parent of one sex. This "chip-off-the-old-block" hypothesis points out that a direct consequence of imprinting is that offspring will phenotypically resemble one parent more than the other, independent of the offspring's sex [...]. A potential scenario for the generation of selection for parental resemblance arises because of the male-biased differential migration rate in most mammals [...]. In a heterogeneous habitat, mothers are likely to be better adapted to the local environment than fathers, because the latter are more likely to have been subject to different selection pressures elsewhere. Thus, at least early in life, before any migration, offspring of both sexes would be selected to resemble their mothers. Thus the chip-off-the-old-block hypothesis would predict that almost any locus exhibiting local adaptation, especially in juveniles [...], could be imprinted. This prediction contrasts with those of the genetic conflict and ovarian time bomb hypotheses that focus on genes active during fetal development and, in the case of genetic conflict, soon after birth.This is an interesting conceptualization, but authors recognize that this hypothesis is unlikely to explain the evolution of imprinting because it requires high levels of recombination and migration; however, this difficulty would prove "why imprinting is not more widespread phylogenetically". The importance here is that these mathematical models would help not only to understand the origin and evolution of the mechanisms of imprinting, but also this may enable predictions.
Spencer HG, and AG Clark. 2006. Genetics 174:931-935
epigenetics
