The hallmark of DNA methylation patterns is the correlation between chromatin and the DNA methylation pattern: its importance for gene expression. Active chromatin is usually associated with unmethylated DNA, while inactive chromatin is associated with methylated DNA.91,102,103 The reiation between DNA methylation, and chromatin structure (referring primarily to the relation between histone proteins and the DNA) has important implications for our understanding of the function of DNA methylation, as well as the processes responsible for generating, maintaining, and altering DNA methylation patterns under physiological and pathological conditions. It was originally believed that DNA methylation precedes and is dominant over chromatin structure.104 Methylation was thought to be generated independently of chromatin structure. Over the course of development, methylation patterns were believed to be laid down shortly after cell replication and to then determine chromatin structure and gene expression. The DNA methylation pattern is proposed to guard the genome from random noise and drift.
