CpG island
From Free net encyclopedia
CpG islands are regions of DNA near and in the promoter of a mammalian gene where a large concentration of CpG sites exist. Unlike CpG sites in the coding region of a gene, in most instances the CpG sites in the CpG islands are unmethylated if genes are expressed. This observation led to the speculation that methylation of CpG sites in the promoter of a gene may inhibit the expression of a gene.
The usual formal definition of a CpG island is a region with at least 200 bp and with a GC percentage that is greater than 50% and with an observed/expected CpG ratio that is greater than 0.6.
External Link: M. D. Anderson Cancer Center