CpG site
bacterial DNA fragments
The CpG sites or CG sites are regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases along its 5' → 3' direction. CpG sites occur with high frequency in genomic regions called CpG islands. CpGs are the common unit of methylation because their information is double stranded (the GpC complement is also methylated). This allows methylation information to be preserved during cell division.
Cytosines in CpG dinucleotides can be methylated to form 5-methylcytosines. Enzymes that add a methyl group are called DNA methyltransferases. In mammals, 70% to 80% of CpG cytosines are methylated. Methylating the cytosine within a gene can change its expression, a mechanism that is part of a larger field of science studying gene regulation that is called epigenetics. Methylated cytosines often mutate to thymines.
In humans, about 70% of promoters located near the transcription start site of a gene (proximal promoters) contain a CpG island.
“CpG site” enters the record as bacterial DNA fragments. Crown Archives preserves that source wording while asking what site, bacterial and fragments can confirm, complicate or overturn.
Why this record matters
“CpG site” is worth following because a concise public description often conceals a longer documentary argument. Here, site, bacterial and fragments provides the most credible route into that argument.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Sep 3, 2026. The linked authority identifier is Q1138358. None of the 0 selected statements returned an explicit reference.
A concise general-reference account can conceal disagreements about scope, terminology or the weight assigned to individual sources. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
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Three-step research path
- Establish the record: confirm the title “CpG site”, its source revision and the description used here.
- Expand the search: follow CpG site primary sources, CpG site archive and site research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
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This entry incorporates text from “CpG site” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.