Genetic imprinting: The battle of the sexes rages on

Genomic imprinting in mammals is an important genetic mechanism by which genes are expressed or repressed depending on which parent they have been inherited from. Some properties of the imprinting mechanism are already established; notably, some of the effects of imprinting on mammalian development can be explained by the phenotypic effects of a number of specific imprinted genes, which include major fetal growth factors. An evolutionary explanation of imprinting has also been suggested. Some of the molecular mechanisms of imprinting are known, and these include the modification of DNA and chromosomes in the form of DNA methylation and possibly heritable chromatin structures. Loss of imprinting or altered imprinting is implicated in a large number of genetic diseases and cancers. Many important issues remain to be resolved; these include the precise molecular mechanisms and, in particular, the nature of the primary imprints that are inherited from the parental gametes, and the genes that control the imprinting process. Isolation of the majority of imprinted genes and the elucidation of their phenotypic effects and physiology are major goals for the future. These studies will provide important insights into human genetics, and will connect evolutionary understanding with physiology, genetic disease and human behaviour.