Poetry of b1 Paramutation: cis- and trans-Chromatin Communication

The term paramutation was coined by Alexander Brinkin the 1950s to describe a meiotically heritable change inthe expression of one allele when it was combined withanother specific allele. In Brink's classic work he proposed that chromosomes possess a paragenetic functionin addition to their genetic one (Brink 1960). Brink distinguished mutations, which arise as discrete events inundirected fashion, are stably transmitted, and are veryrarely reversible, from "paramutations," which occur indirected fashion under specific conditions and are transmitted, but are often unstable, progressively changingback to the original phenotype. Brink was using the term"paramutation" in its broadest sense, equivalent to theterm "epimutation" commonly used today. In addition tothe classic examples of interactions between alleles, paramutation-like interactions have also been described between homologous transgenes or between transgenes andhomologous endogenous genes at allelic or nonallelic positions in a number of species, including plants, fungi, animals, and humans. Thus, a more general definition ofparamutation would be "trans interactions between homologous sequences that set up distinct epigenetic statesthat are heritable through meiosis....