<P> Genomic imprinting is an epigenetic phenomenon that causes genes to be expressed in a parent - of - origin - specific manner . Forms of genomic imprinting have been demonstrated in fungi, plants and animals . As of 2014, there are about 150 imprinted genes known in the mouse and about half that in humans . </P> <P> Genomic imprinting is an inheritance process independent of the classical Mendelian inheritance . It is an epigenetic process that involves DNA methylation and histone methylation without altering the genetic sequence . These epigenetic marks are established ("imprinted") in the germline (sperm or egg cells) of the parents and are maintained through mitotic cell divisions in the somatic cells of an organism . </P> <P> Appropriate imprinting of certain genes is important for normal development . Human diseases involving genomic imprinting include Angelman syndrome and Prader--Willi syndrome . </P> <P> In diploid organisms (like humans), the somatic cells possess two copies of the genome, one inherited from the father and one from the mother . 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%) of genes are imprinted, meaning that gene expression occurs from only one allele . (some recent studies have questioned this assertion, claiming that the number of regions of parent - of - origin methylation in, for example, the human genome, is much larger than previously thought). The expressed allele is dependent upon its parental origin . For example, the gene encoding insulin - like growth factor 2 (IGF2 / Igf2) is only expressed from the allele inherited from the father . </P>

What does a duckling inherit in terms of imprinting