Somatic cell inheritance of methylation patterns. The tags used in this study are unmethylated at birth (unmethylated CpG sites represented by open circles, with filled circles representing methylated sites). Generally the same methylation pattern is faithfully copied and passed on to daughter cells. However, random epigenetic errors may occur, and these errors are also subsequently inherited. Methylation patterns (5' to 3' order of methylation) potentially encode numbers of divisions since birth and ancestral relationships between cells. Of note, new errors in non-stem cells will be lost during normal crypt differentiation, migration and death.