<prompt> Genes in CpP island is inactivated by:MethylationMetrylationUbiquitisationAcetylation  <response>: Ans: a. MethylationRef Lippincott 6th709; Harrison 19th101e-4, 18th668, 679; Robbins 9th893; Satyanarayan 3rd359, 572; Lippincott 4th460-62; Chatterjea Shinde 7th346, 426; en. wikipedia. orgwikiDNA_methylationjCpG islands: Methylation of cytosine by a methyltransferase is associated with silencing of the activities of ceain gene-Lippincott 6th709Cytosine in the sequence CG of DNA gets methylated to form 5-methylcytosine. A major poion of CG about 20 in human DNA exists in methylated form. In general, methylation leads to loss of transcriptional activity thus inactivation of genes.The role of epigenetic control mechanisms in the development of human cancer is unclear. However, a general decrease in the level of DNA methylation has been noted as a common change in cancer. In addition, numerous genes, including some tumor-suppressor genes, appear to become hypermethylated and silenced during tumorigenesis. 