Mechanisms of genomic imprinting

A small number of mammalian genes undergo the process of genomic imprinting whereby the expression level of the alleles of a gene depends upon their p arental origin. In the past year, attention has focused on the mechanisms t hat determine parental-specific expression patterns. Many imprinted genes a re located in conserved clusters and, although it is apparent that imprinti ng of adjacent genes is jointly regulated, multiple mechanisms among and wi thin clusters may operate, Recent developments have also refined the timing of the gametic imprints and further defined the mechanism by which DNA met hyltransferases confer allelic methylation patterns.