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CpG islands are associated with genes, particularly housekeeping
genes, in vertebrates. CpG islands are typically common near
transcription start sites and may be associated with promoter
regions. Normally a C (cytosine) base followed immediately by a
G (guanine) base (a CpG) is rare in
vertebrate DNA because the Cs in such an arrangement tend to be
methylated. This methylation helps distinguish the newly synthesized
DNA strand from the parent strand, which aids in the final stages of
DNA proofreading after duplication. However, over evolutionary time,
methylated Cs tend to turn into Ts because of spontaneous
deamination. The result is that CpGs are relatively rare unless
there is selective pressure to keep them or a region is not methylated
for some other reason, perhaps having to do with the regulation of gene
expression. CpG islands are regions where CpGs are present at
significantly higher levels than is typical for the genome as a whole.
The unmasked version of the track displays potential CpG islands
that exist in repeat regions and would otherwise not be visible
in the repeat masked version.
By default, only the masked version of the track is displayed. To view the
unmasked version, change the visibility settings in the track controls at
the top of this page.
To view the full description, click here.
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