. "The CpG sites or CG sites are regions of DNA where a cytosine nucleotide occurs next to a guanine nucleotide in the linear sequence of bases along its length. \"CpG\" is shorthand for \"\u2014C\u2014phosphate\u2014G\u2014\", that is, cytosine and guanine separated by only one phosphate; phosphate links any two nucleosides together in DNA. The \"CpG\" notation is used to distinguish this linear sequence from the CG base-pairing of cytosine and guanine."@en . . .