Mammalian offspring inherit two versions, or alleles, of each gene, with one allele from each biological parent. However, gene expression is tightly regulated and certain genes undergo the phenomenon of "genomic imprinting," which is where only the allele received by the male or the female parent is expressed. Imprinted genes play diverse roles in development and disruption of their mono-allelic expression can cause diseases, thus understanding the mechanisms behind their regulation is critical. In a recent article published in Communications Biology, a team led by researchers at the University of Tsukuba examined genomic imprinting of a specific genetic locus in mice. Their experiments helped reveal the molecular details of how this mechanism governs expression levels of these genes.