Categorization of CGI probe loci into five distinct classes of DNA methylation propagation.

To determine transgenerational DNA methylation fidelity, methylation levels of specific microarray CGI loci were examined after 1, 3, and 5 cell divisions of the (parental) ovarian cancer cell line A2780. CGI probe loci showing generation-dependent, progressively increased methylation from generations 1 to 5, were defined as the stochastically hypermethylated, while CGI loci showing progressively decreased methylation were considered “stochastically hypomethylated.” Microarray CpG loci demonstrating a mixture of increased and decreased methylation from generations 1 to 5 were considered “randomly methylate,” while CGI loci showing consistently high methylation (>85% of the maximal microarray fluorescence, regardless of generation, also having ≤15% changes between generations) were designated as “heritably highly methylated.” Finally, loci consistently having