Scientists are closer to understanding the mechanisms underlying the phenomenon of genomic imprinting. In this intriguing event, one copy of a gene is 'turned off', or silenced, depending on whether it was derived from the mother or the father. The research team has identified a segment of DNA that is essential in the imprinting process for the closely linked Igf2/H19 genes, two of the first imprinted genes to be discovered. If these genes are incorrectly imprinted, it can lead to the overgrowth (Beckwith--Wiedemann) or dwarfism (Silver Russell) syndromes, and also has a role in some kidney and liver cancers.