Remove 10 μl from each sample into a clean tube and set aside at −20 °C to serve as the 'input DNA control' in Step 27. Set aside ... for which the histone modification status is known.

Histone post-translational modifications are covalent modifications of histones by phosphorylation on serine or threonine residues, methylation on lysine or arginine, acetylation and deacetylation ...