Definition of Cpg Island



CpG Islands are those regions present in a genome that is composed of a large number of dinucleotide repeats of CpGs. They are the stretches of deoxyribonucleic acids that normally have 500 to 1500 base pairs with a CG: GC proportion greater than 0.6. They are typically found at the promotor region and have a 5’ end of the transcript.

 


In the case of the genome of mammals, this region is composed of approximately 300 to 3000 bp and 80% of the CpG nucleotides are methylated. On the contrary, those CGIs which are directly linked to the promotors are not methylated.

 

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