Parental modifiers, antisense transcripts and loss of imprinting

Abstract

The kinship theory of genomic imprinting has explained parent–specific gene expression as the outcome of an evolutionary conflict between the two alleles at a diploid locus of an offspring over how much to demand from parents. Previous models have predicted that maternally derived (madumnal) alleles will be silent at demand–enhancing loci, while paternally derived (padumnal) alleles will be silent at demand–suppressing loci, but these models have not considered the evolution of trans–acting modifiers that are expressed in parents and influence imprinted expression in offspring. We show that such modifiers will sometimes be selected to reactivate the silent padumnal allele at a demand–suppressing locus but will not be selected to reactivate the silent madumnal allele at a demand–enhancing locus. Therefore, imprinting of demand–suppressing loci is predicted to be less evolutionarily stable than imprinting of demand–enhancing loci.