Paramutation and related phenomena in diverse species.

Paramutation describes a process that results in heritable epigenetic changes of gene regulation and trans-homologue interactions. Recent discoveries in model organisms have highlighted roles for the respective nuclear systems that regulate transposons via small RNA molecules both for paramutation and for defining transgenerational inheritance. Differences between plants and animals may influence specific transmission behaviours but the involvement of small RNA-based mechanisms identifies a unifying eukaryotic theme. These mechanisms that specify heritable epigenetic information represent genetic systems adjunct to DNA sequences that contribute to phenotypic diversity.