In the human colorectal carcinoma cell line HCT116, one allele of the p16INK4a gene is not transcribed due to heavy methylation of the associated CpG island, which extends from the promoter to the first intron (Fig. 1)20, 21, 22, 23, and contains H3K9m2, a heterochromatin mark24. This evidence concerns the gene CDKN2A and colorectal carcinoma.