cell harvest and RNA processing. In addition, DNA methylation and expression are fundamentally different measures of cell functional states. DNA methylation levels directly correspond to the number of cells with a methylated/unmethylated cytosine (as a state of methylation of an allele in a particular site is a binary count, in a given cell a site is either methylated or not) whereas protein and mRNA levels are analog measures that average the number of mRNA and protein molecules produced by the cell population. A low level of mRNA or protein measure could indicate either high level of expression in a few cells or low level of expression in many cells.
