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It epigenetic mechanism that produces functional
differences between the paternal and maternal genomes.
Epigenetics defined as heritable changes in gene
activity and expression that occur without alteration in
It require for normal mammalian embryogenesis.
Any disturbance in the imprinting process result in
abnormal embryonic development.
• Silencing occuring through the addition of methyl group
during egg/sperm formation.
• Epigenetic modifiers of gene expression such as DNA
methylation, histone modification, non-RNA and
higher-order chromatin formation.
– Histone acetyl transferases (HATs).
Add acetyl groups to histone tails.
Reduces positive charge and weakens interaction of histones with DNA.
– Histone deacetylases (HDACs).
Removes acetyl groups from histone tails.
Increases interaction of DNA and histones.
Represses transcription (usually).
Involves the addition of a methyl group to DNA.
Usually to the number 5 carbon of the cytosine pyrimidine
Effect: reducing gene expression.
Catalyzed by DNA methyltransferases (DNMTs).
Predominantly found in CpG sites of mammalian genome.
Methylation of CpG sites within the promoters of genes can
lead to their .
silencing, a feature found in a number of human cancers (eg.
silencing of tumor suppressor genes).
• Effects of DNA methylation:
• embryonic development and growth
• Genomic imprinting
• X-chromosome inactivation
IgF2 is an imprinted gene ,being expressed from the
H19 gene is an imprinted gene exprssed only from
Inherit mutated allele from the father
while the allele inherited from the mother
is maturally silenced.
(characterised by hypotonia, obesity,
Inherit mutated allele from the mother while
the allele inherited from the father is maturally
(characterised by epilepsy, tremors, and a
perpetually smiling facial expression)
• It plays an essential role in mammalian
development and growth.
• epigenetic mechanism, mistakes in
maintaining epigenetic mark also cause