Genomic imprinting is a genetic phenomenon by which certain genes are expressed in a parent-of-origin-specific manner. Imprinted genes are either expressed only from the allele inherited from the mother, or in other instances from the allele inherited from the father. Forms of genomic imprinting have been demonstrated in insects, mammals and flowering plants.
In diploid organisms somatic cells possess two copies of the genome. Each autosomal gene is therefore represented by two copies, or alleles, with one copy inherited from each parent at fertilization.
For the vast majority of autosomal genes, expression occurs from both alleles simultaneously. In mammals however, a small proportion (<1%)>
The expressed allele is dependent upon its parental origin. For example, the gene encoding Insulin-like growth factor 2 is only expressed from the allele inherited from the father.
