Genomic imprinting in mammals is an epigenetic mechanism that results in monoallelic, parental-specific gene expression. It affects a subset of genes, primarily those involved in embryonic and neonatal growth, and is maintained through epigenetic modifications such as DNA methylation, long noncoding RNAs (lncRNAs), and histone modifications. Imprinted genes are epigenetically marked in gametes at imprinting control elements (ICEs) and are expressed in a parental-specific manner. These imprints are maintained after fertilization despite extensive reprogramming of the mammalian genome. Genomic imprinting is a key model for understanding mammalian epigenetic regulation. Genomic imprinting is a cis-acting mechanism, meaning it acts on one chromosome. It is not a consequence of sex but of inheritance. Imprinted genes are mostly clustered together with noncoding RNAs and can modify long-range regulatory elements that influence multiple genes. These clusters are regulated by ICEs, which are epigenetic modifications acquired by one parental gamete. The most common ICE is DNA methylation, which is established in either the sperm or oocyte and maintained through cell divisions. It can be erased in the germline to reset the imprint in the next generation. The first three imprinted genes in mice were identified in 1991, showing maternal or paternal expression. These genes are involved in embryonic and neonatal growth, with maternally expressed genes repressing growth and paternally expressed genes promoting it. Imprinted gene clusters contain multiple genes, with some expressed from one parental chromosome and others from the other. These clusters are regulated by ICEs, which control the expression of the imprinted genes. DNA methylation is a key epigenetic modification in genomic imprinting, acting as both an imprinting mark and a silencing mechanism. It is established in either the sperm or oocyte and maintained through cell divisions. It can be erased in the germline to reset the imprint in the next generation. DNA methylation is associated with gene repression and is found in specific regions of the genome called differentially methylated regions (DMRs). These DMRs are either gametic or somatic, with gametic DMRs being established in gametes and maintained in somatic cells, while somatic DMRs are established after fertilization. Imprinted gene clusters contain at least one lncRNA, which plays a role in regulating the expression of the imprinted genes. These lncRNAs are often expressed from the opposite parental chromosome and can act as host transcripts for other regulatory RNAs such as snoRNAs and miRNAs. The role of lncRNAs in genomic imprinting is supported by experiments showing that their deletion leads to the loss of imprinted gene expression. The most common lncRNA in imprinted clusters is H19, which is involved in the regulation of growth and development. Other lncRNGenomic imprinting in mammals is an epigenetic mechanism that results in monoallelic, parental-specific gene expression. It affects a subset of genes, primarily those involved in embryonic and neonatal growth, and is maintained through epigenetic modifications such as DNA methylation, long noncoding RNAs (lncRNAs), and histone modifications. Imprinted genes are epigenetically marked in gametes at imprinting control elements (ICEs) and are expressed in a parental-specific manner. These imprints are maintained after fertilization despite extensive reprogramming of the mammalian genome. Genomic imprinting is a key model for understanding mammalian epigenetic regulation. Genomic imprinting is a cis-acting mechanism, meaning it acts on one chromosome. It is not a consequence of sex but of inheritance. Imprinted genes are mostly clustered together with noncoding RNAs and can modify long-range regulatory elements that influence multiple genes. These clusters are regulated by ICEs, which are epigenetic modifications acquired by one parental gamete. The most common ICE is DNA methylation, which is established in either the sperm or oocyte and maintained through cell divisions. It can be erased in the germline to reset the imprint in the next generation. The first three imprinted genes in mice were identified in 1991, showing maternal or paternal expression. These genes are involved in embryonic and neonatal growth, with maternally expressed genes repressing growth and paternally expressed genes promoting it. Imprinted gene clusters contain multiple genes, with some expressed from one parental chromosome and others from the other. These clusters are regulated by ICEs, which control the expression of the imprinted genes. DNA methylation is a key epigenetic modification in genomic imprinting, acting as both an imprinting mark and a silencing mechanism. It is established in either the sperm or oocyte and maintained through cell divisions. It can be erased in the germline to reset the imprint in the next generation. DNA methylation is associated with gene repression and is found in specific regions of the genome called differentially methylated regions (DMRs). These DMRs are either gametic or somatic, with gametic DMRs being established in gametes and maintained in somatic cells, while somatic DMRs are established after fertilization. Imprinted gene clusters contain at least one lncRNA, which plays a role in regulating the expression of the imprinted genes. These lncRNAs are often expressed from the opposite parental chromosome and can act as host transcripts for other regulatory RNAs such as snoRNAs and miRNAs. The role of lncRNAs in genomic imprinting is supported by experiments showing that their deletion leads to the loss of imprinted gene expression. The most common lncRNA in imprinted clusters is H19, which is involved in the regulation of growth and development. Other lncRN