Many genes have the same function whether they are inherited from the father or the mother. However, few genes are active only when they are inherited from mother & others are active only when they are inherited from father. This fact makes us raise our hands with a few questions: when we recieve genes of same function from both parents, which one’s action will predominate? and what are the basis of this selective predomination of action? Here comes the rule of what is known as “Genetic imprinting” where certain genes inherited from a certain parent will be silenced by an epigenetic mechanism rendering them inactive. This process happens mainly during the development of gametes.

       The fraction of imprinted genes in the human genome is still unknown, however studies refer that 10%-25% of mouse genome is imprinted.

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              Imprinted genes are localized in certain clusters in the genome where the whole cluster is silenced by methylation through certain methylases that act mainly by addition of methyl group to cytosine of spesific CpG dinucleotides within the clusters, so reducing the expression of the rest of genes in the clusters. However, Genetic imprinting is liable to modification along generations, for example if a male recieved imprinted genes from his mother, if it happens that this male will have a daughter, these imprinted genes he recieved from his mother will be activated by another process known as acetylation, where acetylated genes are actively tarnscribed. Thus, whether genes are imprinted or not depends only whether they came from a mother or father & is not a trait being passed through generations ( i.e. Non Mendelian pattern of inheritance). Diseases and developmental disorders are associated mainly when ceratin genes fail to be imprinted. Cancers have deen correlated with failure to imprint growth factors.