Epigenetic modifications such as methylation of CpGs (a dinucleotide composed of a 2'-deoxycytosine and a 2' deoxyguanosine) and histone tail modifications allow activation or repression of certain genes within a cell, in order to create cell memory either in favor of using a gene or not using a gene. These modifications can either originate from the parental DNA, or can be added to the gene by various proteins and can contribute to differentiation. Processes that alter the epigenetic profile of a gene include production of activating or repressing protein complexes, usage of non-coding RNAs to guide proteins capable of modification, and the proliferation of a signal by having protein complexes attract either another protein complex or more DNA in order to modify other locations in the gene.
