The form and function of every living organism on the earth depends on
the complex regulation of gene expression. This is carried out by
controlling and interdigitating spatial and temporal patterns of gene
activity during the life- time of eukaryotic organisms. This is most
dramatically apparent during early stages of development, when new types
of cells and organs are being formed, often during very short time
spans. To achieve this, it is vital that developmentally important genes
can be kept in inactive or active states which are stably inherited in
the soma. Indeed, it is now wellknown that the propen- sity for a gene
to be transcribed or silenced is stably propagated through many cell
generations, even from parent to progeny. This phenomenon constitutes a
type of extragenetic or epigenetic memory of cell identity and
developmental potential which has been fundamental to the evolution of
complex lifeforms, such as the reader of this book. This monograph
focuses on a particular aspect of the epigenetic control of gene
function: genomic imprinting. This defines a phenomenon where some genes
or whole chromosomes can be silenced, activated, or even deleted
depending on their parental origin. The impact of genomic imprinting is
most clearly seen in the areas of cancer, clinical genetics, and
development. Many of the processes associated with genomic imprinting
can be observed in plants, yeast and man, for example, and may
constitute, therefore, principles which are very conserved on an
evolutionary scale.