DNA methylation
DNA methylation is a type of chemical modification which involves the addition of a methyl group to the carbon-5 of the cytosine pyrimidine ring. DNA methylation is probably universal in vertebrates.In humans, approximately 1% of DNA bases undergo DNA methylation.
DNA methylation is an important chemical process of many living organisms. Its importance is further highlighted due to the fact that any disruption to the DNA methylation machinery by gene mutations would result in disability or fatal diseases such as Rett Syndrome or ICF syndrome (immunodeficiency, centromere instability and facial anomalies syndrome).